I tend to have really unusual problems. Unfortunately, this one involves my site now. I don't know if this is the right place to post this, since it's related to XF sorta. I don't think it's an issue with XF itself, though.
I imported all my stuff from phpBB and everything worked well. I noticed that if I delete the folder that contained my phpBB install, XF would not load and I'd get an error message SQL access was denied...on phpBB software.
I'm running an Ubuntu 16.04 server using apache. My vhost file points to the new directory which contains the XF install. Basically, nothing points to my phpBB install location, afaik. But if I delete it, it serves the phpBB error page regarding access denied to the phpbb@localhost mySQL. Interesting to note, I deleted the phpbb user and table in mySQL weeks ago.
It also will happen if I attempt to redirect http to https in my vhost, and will not go away until I load a backup of my vhost file. Even if I remove the redirect entry.
Does anyone have any idea how I could fix this?