When errors pop up on console monitor,SMB shares lose connections, ping times get extremely high, SSH stops responding and jails don't work properly if at all either. Web GUI also becomes inaccessible making a reboot necessary. Starts almost immediately after reboot.
My system is a Dell R720xd with 512GB Ram, a LSi(or compatible) controller for internal drives. The system had no issues until the upgrade to TrueNAS core 12.0
Please see screenshots below and i will try and provide any additional information requested.
Hope my info will help to resolve the issue.