T3 Timeouts Every Few Minutes

I decided to read a bit about cable modem diagnostics today (just for fun!), and it looks like my event logs are filled with the following every few minutes.

15 07/06/20 21:07:09 R05.0 critical Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=68:b6:fc:2e:c0:c9;CMTS-MAC=00:01:5c:70:84:54;CM-QOS=1.1;CM-VER=3.0;
16 07/06/20 21:07:33 R03.0 critical Ranging Request Retries exhausted;CM-MAC=68:b6:fc:2e:c0:c9;CMTS-MAC=00:01:5c:70:84:54;CM-QOS=1.1;CM-VER=3.0;
17 07/06/20 21:07:33 R06.0 critical Unicast Maintenance Ranging attempted - No response - Retries exhausted;CM-MAC=68:b6:fc:2e:c0:c9;CMTS-MAC=00:01:5c:70:84:54;CM-QOS=1.1;CM-VER=3.0;
18 07/06/20 21:07:33 R03.0 critical Ranging Request Retries exhausted;CM-MAC=68:b6:fc:2e:c0:c9;CMTS-MAC=00:01:5c:70:84:54;CM-QOS=1.1;CM-VER=3.0;
19 07/06/20 21:07:33 R06.0 critical Unicast Maintenance Ranging attempted - No response - Retries exhausted;CM-MAC=68:b6:fc:2e:c0:c9;CMTS-MAC=00:01:5c:70:84:54;CM-QOS=1.1;CM-VER=3.0;
20 07/06/20 21:09:09 R05.0 critical Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=68:b6:fc:2e:c0:c9;CMTS-MAC=00:01:5c:70:84:54;CM-QOS=1.1;CM-VER=3.0;

Additionally, I'm noticing the following:

- Downstream power is between -12 and -14 dBmV (too low)

- Downstream SNR always seems to have one channel in the 27-28 range, a few channels in the low 30s and only one value 35+

- Upstream signal strength is 51 dBmV (too high)

Honestly, I'm not experiencing any connectivity issues that I know of, but I am curious as to what is going on and whether any of this is cause for concern. I have internet only (no TV, no voice) without splitters and am using an older, unsupported DOCSIS 3.0 modem (I know, I know). Is the modem the issue?