sdn was one member of the old pool correct?
Nov 1 13:34:42 Arceus kernel: BTRFS info (device dm-10): bdev /dev/mapper/sdn1 errs: wr 1844641, rd 194170, flush 60578, corrupt 2447461, gen 0
Nov 1 13:34:42 Arceus kernel: BTRFS error (device dm-10): parent transid verify failed on 1113877725184 wanted 33563 found 32798
That device looks to be out of sync, the many read and write errors suggest it dropped offline in the past, which device was the other pool member?