A few of my users are unable to use OneAll Steam login to register on my phpbb3 forum. Other users are able to do it just fine.
They click "Register" on my site and then click the Steam icon. The popup appears and they enter their Steam credentials to authorize. Once they click "SignIn", the popup disappears and nothing else happens. We have tried using multiple browsers, disabling adblockers, etc. Nothing seems to work.
I thought it might be the Steam API, but some users can register fine, others can't.