Do you know I have exactly the same problem !  Exactly since upgrading from 4.4.3.1, the devices perfectly for 10-30mins or so and then reboots.  I cant access the web interface but the device will ping via a VPN and other devices will ping.  It's the random reboot that is killing.  I am certain it is a firmware bug.  I pulled some of the logs and got these error messages on failure

20250124_023631_00004859_00007498_QEMU_dies_Ping Fail
20250124_083432_00004859_00007498_QEMU_dies_Ping Fail
20250124_111943_00004859_00007498_QEMU_dies_Ping Fail
20250124_120600_00004859_00007498_QEMU_dies_Ping Fail
20250124_125035_00004859_00007498_QEMU_dies_Ping Fail
20250124_143651_00004859_00007498_QEMU_dies_Ping Fail
20250124_154008_00004859_00007498_QEMU_dies_Ping Fail
20250124_161822_00004859_00007498_QEMU_dies_Ping Fail
20250124_171034_00004859_00007498_QEMU_dies_Ping Fail
20250124_181259_00004859_00007498_QEMU_dies_Ping Fail
20250124_211325_00004859_00007498_QEMU_dies_Ping Fail

I found it was faster to factory reset it and reprogram it by hand. Painful but it will mean a clean slate and hopefully no more corruption.

Did you regress back to 4.4.3.1 ?

No, and I wouldn't. There have been lots of security holes patched in the latest update. If your router is crashing after applying the update, you probably have a corrupt config (don't ask me, that's what Draytek say). So I ended up flashing the firmware with a .rst filename extension to start from scratch. I had to make extensive notes about the setups I look after before starting again, which was painful, but necessary.

The salient question is did that completely resolve the problem of the reboots after 10-30minutes ? I just need to get this one sorted.

Yes.