Aug 26 08:09:13 KeiserUnraid kernel: BTRFS info (device nvme1n1p1): bdev /dev/nvme0n1p1 errs: wr 1929853063, rd 1603059662, flush 20523883, corrupt 0, gen 0
This means device nvme1n1 dropped offline at some point in the post, run a scrub, see here for more info and better pool monitoring.