bad tree block start, want 705757184 have 82362368

[Stephan Olbrich <stephanolbrich@gmx.de>]

Hi,

a few days ago my root file system (simple btrfs on a SSD, no RAID or anything) suddenly became read only. 
Looking at dmsg, I found this:

[   19.285020] BTRFS error (device sda2): bad tree block start, want 705757184 have 82362368
[   19.285042] BTRFS: error (device sda2) in __btrfs_free_extent:6804: errno=-5 IO failure
[   19.285048] BTRFS info (device sda2): forced readonly
[   19.285051] BTRFS: error (device sda2) in btrfs_run_delayed_refs:2934: errno=-5 IO failure
[   19.287213] BTRFS error (device sda2): pending csums is 41889792

Late on I got the same errors for my /home partition (on the same drive) as well.
I have snapshots of all partitions on another drive made by btrbk. To get a working system, I made new (rw) snapshots
of the most recent backup and setup grub and fstab, so my system would boot from the other drive.
Unfortunately now I got the "bad tree block start" error again at least once in dmesg but I didn't save it and it's not in syslog :-(
What I remember is, that it was followed by other btrfs error messages saying something about correcting something.
And the filesystem was still read/write this time.
At the moment I can't reproduce it.

Is there any way to find out, which files are affected by the errors above? I don't really trust the data on the drive I'm using at the
moment, as it has shown errors as well, but I have a less current backup on yet another drive but at it is a few weeks old, I don't
want to use it to setup the system on the SSD again, but just copy the relevant files if possible.
Or is it possible to repair the original file system?

Some information about my system:
Kubuntu 18.04
Kernel 4.19.1 when the problem occured, now 4.19.2
btrfs-tools 4.15.1

Regards,
Stephan