Intermittent drops, Timing sync errors, modem not responsive

Hi there,

Modem is a Motorola MB8600. Router is a Netgear Orbi RBR750. I switched from Google WiFi to the Orbi and enabled LAG on both the modem and router. I am getting downstream 1400Mbps and upstream around 40Mbps. However, every few days, the Internet drops and I cannot reach the modem at 192.168.0.100. Restarting the modem and router usually does the trick, though today DNS did not seem to resolve and I substituted 8.8.8.8 as DNS 1, and now DNS is resolving.

I did find an attenuator in-line with the coax feeding the modem (this is the direct feed from the street). With the attenuator in-line, the OFDM PLC channel power was -1.7dBmV and SNR 37.9dB. Upstream power was around 45-46.5dBmV. No corrected or uncorrected errors. With the attenuator removed, the OFDM PLC channel power is 4.4dBmV and SNR 38.2dB. Again no errors. Upstream power is 38.5-40dBmV. The rest of the stats were pretty consistent (see below - no attenuator).

The current error shown in the modem log is SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing; I can clear the log and all looks good but at some point the modem dies again and the logs seem to clear upon a power cycle.

I've not tried disabling LAG to see if this changes anything. The modem is running firmware 8600-19.3.15, Orbi running V3.2.18.1_1.4.14. I've not tried resetting the modem, just powering it off and on. I could try putting the attenuator back, but I’m worried about the downstream OFDM PLC channel power and I think the upstream power levels are in spec.

Thoughts appreciated.