Time Machine stops after a few gigabytes, without any visible error message
Problem seems to be solved, I am not sure how.


I deleted the erroneus file, but I don't see why it would cause problem in the first place
By a friend's suggestion I've moved physically closer to the Time Capsule, maybe it is getting older and the wifi connection is weaker
I've deleted a volume from boot APFS container (but it wasn't mounted anyway)


I am still somewhat puzzled, but maybe someone coming by with same symptoms can make use of any of these.