MB8611 (customer-owned) stuck on firmware 8611-19.2.18, restarting itself ~2x/day (58 restarts in a month)

Hi, my customer-owned Motorola MB8611 restarts itself about twice a day, and I think it's stuck on old firmware.

Details:

What happens
- The modem fully restarts. Its Ethernet link to my router drops and its uptime counter resets. Each outage lasts about 2 minutes.
- My router logged 58 restarts between Aug 28 and Sep 27 (1–5 per day).
- Most restarts happen a few seconds before :00, :15, :30 or :45 past the hour (for example Sep 27 at 3:14 AM, 11:44 AM and 1:29 PM PT). That looks scheduled rather than random.
- Nothing is logged before a restart. The "SYNC Timing Synchronization failure", "UCD invalid or channel unusable" and occasional "T3 time-out" entries only appear while it reconnects.

Signal looks fine when it's connected
- Downstream SNR about 43 dB, 0 uncorrectables, upstream power about 44 dBmV. The upper downstream channels are around +8 dBmV.

Firmware
- Software version 8611-19.2.18 (Prod_19.2_d31). Other owners here and on Reddit report newer versions (19.2.20, 21.3.7) and the same restarts on 19.2.18, including firmware updates that fail and keep retrying.

Already tried
- A different wall outlet (about 13 more restarts since), new cables, and a technician visit. The technician thought the modem was the problem. I've also ordered a replacement power adapter.

Also: my account seems to list the wrong device, a gateway MAC that isn't my modem.

Could you please:
1. Check whether firmware updates are being sent to my modem and failing
2. Get it onto the current approved firmware, or stop any failing retry loop
3. Correct the device listed on my account

I can send the modem's MAC, serial number and a full timestamped restart log by private message.