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Upgrade from Arris S33 to new Arris S34: Frequent "Loss of Sync" and upstream channel flapping
I recently decided to upgrade from my Arris S33 to an Arris S34 to take advantage of the mid-split upload speeds rolled out to our area (Seattle 98102) some time ago.
I'm able to provision the modem, and it sort of works, but I observe frequent, brief disconnects. These correspond to “Loss of Sync” error messages in the Cable Modem event log. Every "Loss of Sync" event corresponds to a missed ping when I run a ping process on the laptop attached to the modem. These loss of sync messages occur 2-3 times per minute.
In this state the connection is somewhat usable, but very unstable. I can browse the web, but things like streaming audio end up experiencing frequent cuts/drops.
I live in a group of 6 town townhomes, grouped 3 front 3 back. The service to the townhomes in the back comes from a single cable that is split by a BDS103BH 3-way splitter to each of the 3 individual townhomes. To the best of my knowledge, this splitter was installed when the townhomes were built back in 2015. It's a 1000MHz balanced 3-way splitter.
To eliminate building wiring as an issue, I tried connecting my modem directly to the splitter output for my unit. In this configuration, I still observe the problem, although it's slightly less frequent (once every 1-2 minutes, instead of 2-3 times per minute).
Is there anything else I can investigate on my own, here? Is there enough information to warrant a line tech to come check things out?
FOOTNOTES
LOG EXAMPLE (Arris S34 Loss of Sync - just the last few minutes while writing this message)
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09/23/2026 18:55:58 |
Critical |
SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Notice |
CM-STATUS message sent. Event Type Code: 2; Chan ID: 2; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Critical |
SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Notice |
CM-STATUS message sent. Event Type Code: 2; Chan ID: 7; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Critical |
SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Notice |
CM-STATUS message sent. Event Type Code: 4; Chan ID: 4; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Warning |
Lost MDD Timeout;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Notice |
CM-STATUS message sent. Event Type Code: 16; Chan ID: 193; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 3.;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Warning |
Lost MDD Timeout;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Critical |
SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Notice |
CM-STATUS message sent. Event Type Code: 2; Chan ID: 1; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Critical |
SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Notice |
CM-STATUS message sent. Event Type Code: 2; Chan ID: 3; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Critical |
SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Notice |
CM-STATUS message sent. Event Type Code: 2; Chan ID: 1; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Critical |
SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Notice |
CM-STATUS message sent. Event Type Code: 16; Chan ID: 193; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 3.;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Critical |
SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Notice |
CM-STATUS message sent. Event Type Code: 2; Chan ID: 4; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Critical |
SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Notice |
US profile assignment change. US Chan ID: 41; Previous Profile: 12; New Profile: .;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Critical |
SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Notice |
CM-STATUS message sent. Event Type Code: 2; Chan ID: 3; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Critical |
SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Notice |
CM-STATUS message sent. Event Type Code: 2; Chan ID: 3; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Critical |
SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Notice |
CM-STATUS message sent. Event Type Code: 5; Chan ID: 17; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Critical |
SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Notice |
CM-STATUS message sent. Event Type Code: 16; Chan ID: 193; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 3.;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Critical |
SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Notice |
CM-STATUS message sent. Event Type Code: 2; Chan ID: 3; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Critical |
SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Notice |
CM-STATUS message sent. Event Type Code: 5; Chan ID: 12; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
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Critical |
SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=[Edited: “Personal Information”];CMTS-MAC=[Edited: “Personal Information”];CM-QOS=1.1;CM-VER=3.1; |
CHANNEL STAUS EXAMPLE (Arris S34)
Here is an example of the channel status. Note: The Upstream Bonded Channel flaps. When I refresh, sometimes there are 0 channels, 3 channels, 4, or 5 channels. It’s constantly updating. This is an example I caught when 5 were up.
Procedure Status Comment
Acquire Downstream Channel 453000000 Hz Locked
Connectivity State OK Operational
Boot State OK Operational
Configuration File OK
Security Enabled BPI+
DOCSIS Network Access Enabled Allowed
Downstream Bonded Channels
Channel ID Lock Status Modulation Frequency Power SNR/MER Corrected Uncorrectables
12 Locked 256QAM 453000000 Hz -2.4 dBmV 43.4 dB 4982 37869
1 Locked 256QAM 387000000 Hz -3.0 dBmV 43.4 dB 8135 51733
2 Locked 256QAM 393000000 Hz -3.0 dBmV 40.9 dB 8401 47443
3 Locked 256QAM 399000000 Hz -3.1 dBmV 43.4 dB 7742 50308
4 Locked 256QAM 405000000 Hz -2.9 dBmV 43.4 dB 7567 44461
5 Locked 256QAM 411000000 Hz -2.9 dBmV 43.4 dB 7647 47879
6 Locked 256QAM 417000000 Hz -3.0 dBmV 43.4 dB 8887 50734
7 Locked 256QAM 423000000 Hz -2.8 dBmV 40.9 dB 5399 45022
8 Locked 256QAM 429000000 Hz -2.7 dBmV 43.4 dB 6443 39304
9 Locked 256QAM 435000000 Hz -2.7 dBmV 43.4 dB 5684 37211
10 Locked 256QAM 441000000 Hz -2.7 dBmV 44.6 dB 6015 39837
11 Locked 256QAM 447000000 Hz -2.7 dBmV 43.4 dB 6047 37477
13 Locked 256QAM 459000000 Hz -2.5 dBmV 43.4 dB 5988 36836
14 Locked 256QAM 465000000 Hz -2.5 dBmV 43.4 dB 5808 38937
15 Locked 256QAM 471000000 Hz -2.6 dBmV 43.4 dB 5378 37876
16 Locked 256QAM 477000000 Hz -2.6 dBmV 43.4 dB 6372 40011
17 Locked 256QAM 957000000 Hz -5.6 dBmV 40.9 dB 6158 40902
18 Locked 256QAM 963000000 Hz -5.6 dBmV 40.9 dB 5828 42376
19 Locked 256QAM 969000000 Hz -5.5 dBmV 40.9 dB 5851 45135
20 Locked 256QAM 975000000 Hz -5.7 dBmV 40.9 dB 5961 44057
21 Locked 256QAM 981000000 Hz -5.8 dBmV 40.4 dB 5931 43850
22 Locked 256QAM 987000000 Hz -5.7 dBmV 40.4 dB 6201 44288
23 Locked 256QAM 993000000 Hz -5.8 dBmV 40.4 dB 6449 49286
24 Locked 256QAM 999000000 Hz -5.9 dBmV 40.4 dB 6335 52266
193 Locked OFDM PLC 774000000 Hz -3.4 dBmV 44.0 dB 3293192 513
Upstream Bonded Channels
Channel ID Lock Status US Channel Type Frequency Width Power
4 Locked SC-QAM 35600000 Hz 6400000 44.0 dBmV
1 Locked SC-QAM 16400000 Hz 6400000 43.0 dBmV
3 Locked SC-QAM 29200000 Hz 6400000 43.8 dBmV
2 Locked SC-QAM 22800000 Hz 6400000 43.5 dBmV
41 Locked OFDMA 36200000 Hz 44400000 38.2 dBmV
XfinityRay
Official Employee
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4.3K Messages
5 hours ago
Hi there, @jibbl! Thanks for all the information you shared about your service. This is sounding like most likely, we need a visit. The loss syncs and splitter are both sticking out and very concerning to me. Our technician would run thorough testing to find the root cause and repair it. Were you getting any disconnects with the S33 or not that you had noticed?
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