It's not an fs corruption problem, why I asked for diags after array start:
Mar 26 09:53:38 unRAID root: mount: /mnt/disk1: unknown filesystem type 'xfs'.
This happened one time before, it's like xfs is not installed, don't remember exactly what the problem was, but probably a corrupt Unraid install, take the opportunity to upgrade to v6.8.3 and reboot.