The file size dimensions are currently 128x128, but if you upload something smaller, say for example 125x125, you get a notice telling you
"The avatar dimensions are under the allowed minimum dimensions."
Which is to be expected (it works by design). However, upon receiving this notice, if you upload the correct file size, you'll discover that sometimes nothing happens. The notice remains and your new avatar is not displayed. Only a page refresh or navigating away, then back... Resolves it.
This is not easy to reproduce and it only happens, sometimes (reasons unknown). As such I do not see it as a problem (non-critical) and only an occasional annoyance. But thought to report it, just the same.