Doesn't look like a disk problem to me, it was mounting before with unencrypted xfs:
May 6 18:35:28 Unraid unassigned.devices: Adding disk '/dev/sda1'...
May 6 18:35:28 Unraid unassigned.devices: Mount drive command: /sbin/mount -t xfs -o rw,noatime,nodiratime '/dev/sda1' '/mnt/disks/Intenso_External_USB_3.0'
May 6 18:35:28 Unraid kernel: XFS (sda1): Mounting V5 Filesystem
May 6 18:35:29 Unraid kernel: XFS (sda1): Ending clean mount
Then it didn't mount with encrypted xfs, does it still work if you reformat without encryption?