I just found something really strange, it seems pointers for extent tree and csum tree have somehow gotten swapped...
$ btrfs inspect dump-super -f /dev/sda | grep backup_extent_root backup_extent_root: 21056867106816 gen: 2262737 level: 3 backup_extent_root: 21056867762176 gen: 2262738 level: 3 backup_extent_root: 21057133690880 gen: 2262740 level: 3 << points to CSUM_TREE backup_extent_root: 21056854228992 gen: 2262736 level: 3 $ btrfs inspect dump-super -f /dev/sda | grep backup_csum_root backup_csum_root: 21056868122624 gen: 2262737 level: 3 backup_csum_root: 21056944685056 gen: 2262738 level: 3 backup_csum_root: 21057139916800 gen: 2262740 level: 3 << points to EXTENT_TREE backup_csum_root: 21056857341952 gen: 2262736 level: 3 $ btrfs inspect dump-tree -b 21057133690880 /dev/sda | head -n 2 btrfs-progs v5.10.1 node 21057133690880 level 1 items 316 free space 177 generation 2262698 owner CSUM_TREE $ btrfs inspect dump-tree -b 21057139916800 /dev/sda | head -n 2 btrfs-progs v5.10.1 leaf 21057139916800 items 166 free space 6367 generation 2262696 owner EXTENT_TREE Previous gen is fine $ btrfs inspect dump-tree -b 21056867762176 /dev/sda | head -n 2 btrfs-progs v5.10.1 node 21056867762176 level 3 items 2 free space 491 generation 2262738 owner EXTENT_TREE $ btrfs inspect dump-tree -b 21056944685056 /dev/sda | head -n 2 btrfs-progs v5.10.1 node 21056944685056 level 3 items 5 free space 488 generation 2262738 owner CSUM_TREE Also generation specified in backup root doesn't match with one in block so seems like latest gen wasn't written to disk or something like that. In root tree there is different extent tree used than one specified in backup root. $ btrfs inspect dump-tree -b 21057011679232 /dev/sda | head -n 6 btrfs-progs v5.10.1 node 21057011679232 level 1 items 126 free space 367 generation 2262739 owner ROOT_TREE node 21057011679232 flags 0x1(WRITTEN) backref revision 1 fs uuid 8aef11a9-beb6-49ea-9b2d-7876611a39e5 chunk uuid 4ffec48c-28ed-419d-ba87-229c0adb2ab9 key (EXTENT_TREE ROOT_ITEM 0) block 21057018363904 gen 2262739
