Thanks @JorgeB,
I configured the share to move everything off the cache nvme, and after multiple forced restarts mover did it's thing. Right now I destroyed the pool, removed the cache share and rebooted from the gui. Looks promising. The array stopped and the server rebooted without a hitch. Searching in the syslog I can't find a panic anymore.
Fingers crossed that was the problem.
Thank you very much!