Sudden, Frequent Cable Modem Reboots

I have had extrordinarily stable cable modem service from Comcast for many years, running on a SB6141 cable modem (customer owned).

 

About two weeks ago, I started having frequent, short lived outages... Several a day at random times, though it really seems to like to go down around 4:30pm.  However, I see the reboots happen at various other times.

 

My cable modem power and signal to noise levels are within spec and I get good upload/download speeds any time I've tested.

 

A sample of my logs looks like so:

 

Z00.0 MIMO Event MIMO: Stored MIMO=-1 post cfg file MIMO=-1;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
N/A Cable Modem Reboot due to T4 timeout ;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
R04.0 Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
R02.0 No Ranging Response received - T3 time-out;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
R06.0 Unicast Maintenance Ranging attempted - No response - Retries exhausted;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
R03.0 Ranging Request Retries exhausted;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;

 

What should I start looking at?