I’m having the same problem. I think it appeared a couple betas ago. I first noticed it when there were no avatars to choose from (as described in Selectable avatar quirks), but now there are avatars added and I get the same empty “change your profile picture.” I tried safe mode, but there are a bunch of plugins that could be causing a problem.
The solution I’m attempting is to convince the site admin that forcing people to use a set of avatars is a bad idea. 