Problem was caused by one of the cache devices dropping offline:
Apr 4 18:50:50 M1171-NAS kernel: ata1: softreset failed (1st FIS failed)
Apr 4 18:50:50 M1171-NAS kernel: ata1: limiting SATA link speed to 3.0 Gbps
Apr 4 18:50:50 M1171-NAS kernel: ata1: hard resetting link
Apr 4 18:50:55 M1171-NAS kernel: ata1: softreset failed (1st FIS failed)
Apr 4 18:50:55 M1171-NAS kernel: ata1: reset failed, giving up
Apr 4 18:50:55 M1171-NAS kernel: ata1.00: disabled
There's a known issue with the onboard SATA controller in some Ryzen boards, look for a BIOS update, or use an add-on controller.
The problem is the filesystem in the destination disk:
Apr 3 20:28:07 Tower kernel: REISERFS error (device md9): vs-5150 search_by_key: invalid format found in block 232203785. Fsck?
Apr 3 20:28:07 Tower kernel: REISERFS (device md9): Remounting filesystem read-only
Also good idea to convert all reiserfs disks to xfs, reiserfs is not recommended for v6.
This is a Linux/LSI issue, not Unraid, at the time I tried with Arch Linux and it had the same problem, which is not surprising since Unraid uses a standard kernel.
Also, very easy to flash an LSI, you can do it using Unraid.
Apr 1 08:33:13 Vault emhttpd: unclean shutdown detected
A few sync errors after an unclean shutdown are expected, if you haven't yet run a correcting check.
Still showing some ATA errors, you should replace cables.
Looks more like a connection problem, replace cables on that disk and try again.
If you mean the UDMA_CRC errors those are a connection problem, usually the SATA cable.