btrfs check --repair /dev/mapper/pool2

[3/7] checking free space cache
cache and super generation don't match, space cache will be invalidated

It is not real problem, but cache can be cleared:

btrfs check --repair --clear-space-cache v1 /dev/mapper/pool2

enabling repair mode
Opening filesystem to check...
Checking filesystem on /dev/mapper/pool2
UUID: 947b20e3-bc05-4f85-8989-d19178506209
Free space cache cleared

btrfs check --repair /dev/mapper/pool2

[4/7] checking fs roots
root 649 inode 418 errors 1040, bad file extent, some csum missing
root 649 inode 419 errors 1040, bad file extent, some csum missing
ERROR: errors found in fs roots

Mount filesystem and find files belonging to inodes.

find /mountpoint -inum 418 -print

Find will report multiple files located on multiple subvolumes with the same inode. List subvolumes to get root id:

btrfs sub list /mountpoint

<code> ID 257 gen 524652 top level 5 path @volume ID 258 gen 524651 top level 257 path @volume/subvol1 ID 649 gen 524652 top level 257 path @volume/subvol12 <code>