Some users might have experienced an issue where the avatar can't be changed anymore. The new avatar is visible in the upload window but not in the icon in their channel or in the upper right corner.
This is simply a cache issue. If you experience this problem please try a different browser or private/incognito mode in your current browser. If the avatar is visible there it is a common cache issue.
You have to clear your browser cache via settings to make it visible. Another approach would be to log in multiple times to force your browser to refresh the cache.
Don't worry! Even if you can not see the updated avatar everyone else is already able to see it.