Cache filesystem is corrupt:
Mar 21 21:09:13 UNRAID kernel: REISERFS error (device sdh1): vs-5150 search_by_key: invalid format found in block 18130149. Fsck?
Mar 21 21:09:13 UNRAID kernel: REISERFS (device sdh1): Remounting filesystem read-only
You need to run a filesystem check or better yet take to opportunity to convert o XFS, reiserfs is not recommended.
You can, you'd need to do a new config, but for parity to still be 100% in sync with the old disk the rebuild would need to be done in maintenance mode.
Yes
Not seeing the reason why, please reboot and post new diags after array start (there shouldn't be one but if there is a "all data on this device will be delete" in front to the cache pool device(s) don't start the array).
You should first try to find out why it got disable, or post the diagnostics, but if you just want to re-enable:
-stop array
-unassign parity
-start array
-stop array
-re-assign parity
-start array
That is the correct driver, still need to check it's in IT mode and using latest firmware, you can see that on the syslog, or post it here.
You'll need to re-assign all the disks to their original positions.
Most likely some issue with the Realtek driver, it's not the first time, you'll need to wait for an update, LT usually uses the latest driver available.