[WebDev WaxLotus LLC]

All fixed. This post by deadmedic fixed all my issues! It explains why all the ‘worked for me!’ posts seemed like nonsense to me.

The fix:

Change line 673 in bb-settings.php from:

$bb->sitecookiepath = rtrim($bb->sitecookiepath, '/');

to:

$bb->sitecookiepath = '/' . trim($bb->sitecookiepath, '/');

Thank you deadmedic!