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

Root number is subvolume id number, so mount subvolume to find files belonging to inodes

mount /dev/mapper/pool2 -o subvolid=649 /mountpoint
find /mountpoint -xdev -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

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
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====== Rescan hasn't been ======
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[7/7] checking quota groups
Rescan hasn't been initialized, a difference in qgroup accounting is expected

btrfs quota rescan /mountpoint