I would ssh into the opnsense box and press 8 to run the shell terminal and then run dmesg and go back to the time the server rebooted, there you can see the events leading up to the shutdown.
That’s awesome, best of luck it stays that way!
Dang, how does your isp feel about that many machines talking out to the internet, have they made you pay for business plans yet?
If you want privacy try njalla. A bit more expensive but they do try hide as much data as possible and I’ve never had any downtime with them.
The way I get around the syncing issue is to set my syncthing to sync when my phone is charging so it’s very unlikely to not be in sync, or if I change a password on the PC I’ll plug my phone into a USB and it syncs straight away.
I also use KeepassDX on Android and never have those issues.