Asterisk thinks phone is registered, but phone does not

FPBX distro
Yealink T46G (some with 4-5x EPX40 modules).
Commercial EPM
System has been in … semi-production (migration) for almost a month.

Occasionally, a few of our phones will not reconnect properly to FPBX. According to PBX logs, the phone is connected. The phone itself shows “Register failed” but if I check it’s ext’s status on my phone or in asterisk, it shows as connected and available.
This seems to occur after a reboot, and happens more often during a mass reboot. We had to power everything down on Friday evening, and everything came back up on Saturday morning. 98 of our phones reconnected fine, but our reception phone cacked out. As this was our reception phone, I didn’t have time to download it’s logs (will do so next time a less critical phone fails). Rebooting the phone solved the issue.

The thing is, this sort of thing seems to happen very often. Phones will say Register failed, when asterisk is seeing it connect. Asterisk continues communication with the phone the entire time. Sometimes the phone will register fine, but none of it’s BLF’s will work. Phone can call out but BLF’s are either all off, or red (indicating it believes all monitored extensions are in use).

Any idea’s? Yealink support of course, is non-existent.