Forum is broken when loading from Facebook

FORUM: [login to view URL] Hi there. I have spent weeks trying to figure this problem out, but I am going in circles. IPB support recommended I open a thread here because they are convinced the error is theme related. The theme developer says it's not the theme that is causing the issue. The firewall company, Sucuri, says it's not their fault either. I am out of options on where to turn, maybe you guys can help. (Error attached) When some users (Android) click a link from Facebook to my forum, they see this: [login to view URL] I believe the error started to occur after SSL was enabled and is causing some mixup with Facebook's browser. Again, Sucuri, the company that added the SSL certificate, says it's not their fault but I can't confirm one way or the other. Does anyone have *any* idea what could be causing this error? I would be so, so appreciative if someone could help me fix this.