Not a known problem, but we'll definitely look into it. Our automated tests don't have an issue with this, so it may be unique to your site.
Another thing to try, if you don't mind, is on our demo site which runs 4.0.1. If you run into the issue there, definitely let us know as it may be account specific, but other avatars seem to be coming in.
www.sourcecoast.com/jfbconnect/demo
JomSocial Home page on the demo site:
www.sourcecoast.com/jfbconnect/demo/jomsocial-home-page
With that said, can you let me know what JS version you're using? Also, did this seem to work in 4.0.0 or did you upgrade straight from 3.4 (which should be fine).
Finally, another test is to clear your Joomla cache as well as your browser cache. The Joomla cache has been causing a few users problems, especially if they're using a minification extension to combine Javascript files.
Thanks,
Alex