unscheduled system reboot

May be for some services, like Windows domain or Kerberos, but it should not cause anything like the kernel panics.

ok, we'll start with that, just a comment to provide some information, today we realized that the bios clock was ahead of 3:00 HS, in the bios it had 17:28 and in the truenas it was set at 14:28, which is the correct time in our area. this can generate some errors, right?

As I have told, start from cleaning, cooling and 24 hour long memory test.

I thank you in advance for the time invested in this case and the advice that will be carried out. On the other hand, could you tell me, if possible, what are the hardware resources that generated the events? to focus on those areas and test them in depth. On the other hand, at this moment the system has generated an error in the console that says: File "/us/local/lib/python3.9/site-packages/middlewared/client/client.py", line 124, in connect self .sock.connect(self.bind_addr) ConnectionRefusedError: [Errno 61] Connection refused, and we can't access it via the web, but we can access the files that are in an NFS resource created on the system.

In the debug provided I see 5 kernel dumps, and all of them are different. Despite this system having ECC memory, that would be my first guess, it must be something with hardware. Considering this is a very old system, I would recommend to clean it properly, check its cooling, update BIOS and firmwares and run good long memory test. I can not start debugging everything same time, there was not so many difference between U51 and U5.3 to cause all those problems.