Hello @alejandro.aguilar
You might want to log into the CIMC and go through the event log to see whether it was in any way related to a hardware failure (unlikely - the SNS is quite reliable - but worth checking).
It's more likely that the ISE application had a crash and then rebooted. Have you looked into the ISE GUI Alarms panel to see if there are any clues? Go into the node's CLI and check the disk space. Also check if there are any crash logs on the CLI. ISE sometimes leaves clues around. But a spontaneous reboot is not that common. You might also want to check the Admin Reports to see if anyone triggered a reboot?
I think the TAC can analyse the crash dumps to give you the root cause.
ISE has many logs - you could create a support bundle in ISE, download it and analyse it for days - or save yourself the heartache and open a TAC case.
