Januszmirek

So I finally solved the issue. Turns out it wasn't a corrupt docker image or a problem with docker networks or anything else that I initially suspected. One other issue I was encountering for months now (but somehow did not connect it with this one) is that every night I got notifications about cache disk space filling out (to 100%). I had no idea what was this about as in the morning everything was fine and cache disk was maybe 60% filled. I then forgot I created about 600gb VM on my array - the space i needed for it was too big for my cache. What I however forgot to change after creating the vm was to not attempt moving the VM to cache. Basically as show below:

 
I really did not need this VM anymore, so deleted it and boom! all problems magically disappeared all together. No more btrfs or syslog errors.
Doubt this would help anyone, but just wanted to let you know the issue is resolved.