From what I've seen and tried I think it might be the directory. The forum link changed when we swapped over not too long ago. So links for everything are kinda broken. Click "Forum" tab on the forum and it'll be on the old version where it has you logged out. Click the smaller forum tab underneath where it says "New Posts" and it'll take you to the new and current site. Click Members and it'll have you logged out and on the old version logged out, but click a new page (I.e: page 2 for viewing more members) and you're logged back in.

I think there's just a lot of broken links to take you to the correct place it's trying to take you. Logging you back out in the old version vs the new one.

If you're on your phone. Go to Home, then open the forum from there. Log in (may have to go to the full page login and not the one up top that'd be easier. Once logged in it may not look like you are. Go to a random thread and click the smaller "Forum" tab below the "New Posts" box. It should take you to the main and current forum with you logged in.