I spent several hours on this issue, but couldn’t find a solution. Restoring from backup didn’t help either 
Found this issue from 2018: How to fix user avatar?
As far as I can tell, the problem there was some incompatibility between Discourse’s internal components. Can I experience something similar? TBH, I would expect a problem in Discourse to affect many more installations, but the aforementioned problem involved just one reporter as well.
I’ll appreciate any help 