Very slow Internet Download Speeds even after Xfinity repairs in my area

Even after Xfinity completed repairs in my area for performance related issues and even though I worked with Xfinity support, I continue to get extremely slow internet download speeds (about 10-20% of my provisioned speed).

Generally speaking, my upload speed via Speedtest.net have stayed well within my 20 Mbps provisioned speed. My download speed via Speedtest.net, which is provisioned for either 800 or 900 Mbps, dropped very low providing only 10-20% of my provisioned speed.

As I write this post, I continue to see these extremely slow speeds . I'm troubleshot this issue with Xfinity support (Ticket Number: [Edited: "Personal Information"]) and this post is part of that troubleshooting effort, although I encourage anyone with any insights into this problem to offer assistance.

My cable modem is a Netgear CM1000.

Below are extensive details about the issue.

Cable Modem Details

Netgear CM1000

Logs (after rebooting the cable modem)

Note that the logs are captured across two images

Here are the logs in text format.

2024-12-20, 20:48:43 Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-20, 20:48:42 Notice (6) DS profile assignment change. DS Chan ID: 33; Previous Profile: ; New Profile: 1 2 3 .; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-20, 20:48:41 Notice (6) DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3 .; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Notice (6) Honoring MDD; IP provisioning mode = IPv6
Time Not Established Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-20, 16:57:49 Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-20, 16:56:19 Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-20, 16:49:56 Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-20, 16:49:55 Critical (3) No Ranging Response received - T3 time-out; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-20, 16:49:52 Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-20, 15:52:02 Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-20, 15:50:57 Critical (3) Resetting the cable modem due to docsDevResetNow
2024-12-20, 15:31:06 Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-20 15-30-01 Critical (3) Resetting the cable modem due to docsdevResetNow
2024-12-20, 12:57:14 Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-19, 12:23:27 Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-19, 12:23:26 Critical (3) No Ranging Response received - T3 time-out; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-19, 12:23:19 Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-19, 12:23:19 Critical (3) SYNC Timing Synchronization failure - Loss of Sync; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-19, 12:22:56 Critical (3) UCD invalid or channel unusable;CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1;
2024-12-19, 12:18:37 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-19, 12:18:32 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-19, 12:18:32 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-19, 12:18:31 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-19, 12:18:29 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-19, 12:18:28 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-19, 12:18:26 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1

Connection Information

Note that the connection information is captured across two images

Timeline Details

Yesterday I received a text message at 12:17 pm from Xfinity stating that there were performance issues in my area and work was being done to revolves these issues.