Endless mount and backpointer mismatch

[Pepie 34 <pepie34@gmail.com>]

Dear BTRFS community,

I've a raid 1 setup on two luks encrypted drives for 4 years that serves
me as btrbk backup target from an other computer.
There is a lot of ro snaptshots on it.

I've mistakenly launched a balance on it which was extremely slow and
tried to cancelled it.
After two days of cancelling without results, I decided to power off the
computer.

After the reboot, even with the skip_balance mount option, the mounting
is endless, no error in the kernel message and it never mounts.

What I have done so far:
- mount the volume with the ro option (fast to mount, data OK).
- scrub in ro mode, no error found
- btrfs check
In the extent check  there is plenty of errors like this :
=>
ref mismatch on [9404816285696 32768] extent item 6, found 5

incorrect local backref count on 9404816285696 parent 5712684302336
owner 0 offset 0 found 0 wanted 1 back 0x55f371ee1ad0
backref disk bytenr does not match extent record, bytenr=9404816285696,
ref bytenr=0
backpointer mismatch on [9404816285696 32768]
<=
No errors in other checks, though checking "quota groups" is very slow.

What should I do ? btrfs check --repair ?
btrfs check --init-extent-tree ?
btrfs --clear-space-cache ?

Will the "init extent tree" option break btrfs receive with old snapshot
parents ?

Best regards,

Pepie34