It's really a weird bug. In the group profile page, when the user hover and click on a member's avatar, the hover dropdown menu does not appear. What's even more weird is that this only happens in a few groups and other groups are woking fine. 

I checked the network, the menu/user_hover/contents ajax request is successully sent and other query strings are also in the request, but it doesn't return anything. the preview and response tab in chrome dev tool is empty. The code for this part should be the same across the site, right? Why is it behaving differently in different groups? Any ideas will be appreciated.