Both TV boxes recently started randomly going out, getting stuck in reboot loop

Internet service is fine, including streaming Xfinity TV programs. But TV service has recently stopped working reliably, within the last week or so

- two boxes: main X1 box in living room, secondary box (smaller, don't know the model type) in office

Sometimes TV is working fine. Other times I turn on the TV and it just shows the "Welcome. Bienvenido. Bienvenue.". So it seems to be randomly rebooting at times when I'm not watching.

A few times, I've been watching a show, and it seems to start glitching, then the box reboots after 20-30 seconds.

The office box sometimes shows error RDK-03036. I have power-cycled both boxes multiple times, doesn't seem to make a difference.

To my knowledge, nothing has changed with the hardware or cabling within the house. No issues with internet, as mentioned -- consistently getting good speeds.