But before that, would you mind to run "btrfs check" again on the fs to
see if it reports any error?

I'm interested to see the result though.

First I will send you the full output of the command I ran:
btrfs check --repair --init-csum-tree /dev/mapper/xyz
It's a lot of output - around 50MB before I zip it up.
How about if I send that to you as an attachment and mail it directly
to you, not the list?

Next step: I have remounted the old fs and I'm going to run a scrub on it.

Then I will unmount it and run btrfs check again and send you the
output. Again, I'll send it to you privately, OK?