This can be due to incorrect file permissions preventing profile pictures cache from working properly. To resolve/debug this issue, please click on the profile picture to check what errors you get in the address bar.
Before trying the following solution please make sure that gravatars is turned on under your WordPress > Discussion Settings
Go to Settings -> Compatibility Settings -> Toggle URL Encodings value.
If still problem persists, please make sure you have the following on your server:
- GD library is installed and running properly on your server
- PHP version 5.0 or better
- You have write permissions to the cache folder as explained above
- rename(), file_put_contents(), move_uploaded_file() PHP functions are enabled by your server and working properly
If you’ve done all that, and cannot get thumbnails to work, please submit a topic