Pool was working correctly but one of the devices dropped offline:
Oct 8 02:41:06 UnCRATE kernel: ata1.00: revalidation failed (errno=-19)
Oct 8 02:41:06 UnCRATE kernel: ata1.00: disabled
Oct 8 02:41:06 UnCRATE kernel: sd 1:0:0:0: rejecting I/O to offline device
Oct 8 02:41:06 UnCRATE kernel: blk_update_request: I/O error, dev sdi, sector 71914232 op 0x1:(WRITE) flags 0x8800 phys_seg 1 prio class 0
Oct 8 02:41:06 UnCRATE kernel: BTRFS error (device sdi1): bdev /dev/sdi1 errs: wr 1, rd 0, flush 0, corrupt 0, gen 0
Oct 8 02:41:06 UnCRATE kernel: blk_update_request: I/O error, dev sdi, sector 71914248 op 0x1:(WRITE) flags 0x8800 phys_seg 1 prio class 0
Oct 8 02:41:06 UnCRATE kernel: BTRFS error (device sdi1): bdev /dev/sdi1 errs: wr 2, rd 0, flush 0, corrupt 0, gen 0
Oct 8 02:41:12 UnCRATE kernel: ata1: hard resetting link
Check replace cables for sdi then post new diags.