When I edit the php to run 7.4 or newer I can't log in (nor can anyone else). If I am logged in and upload the .htaccess with the new handler then the board runs fine on 7.4 but if I log out I can't get back in. I put it back to 7.3 and everyone can get in again.
I can't keep running 7.3 much longer as a couple of heavily used plugins in wordress have stopped working completely while on 7.3 (Events being the main one).