Updated to 12.0 U2 and received the following email alert:
* System core files were found in /var/db/system/cores. Please create a ticket at https://jira.ixsystems.com/ and remove these files.
After i paste ls -l /var/db/system/cores in the shell i get this:
-rw------- 1 root wheel 274808832 Apr 6 18:27 python3.8.core
I get random reboots and don't know how to proceed now.