Indeed, we are still having random issues since Sunday afternoon on April 30th. So, I really feel for people that are convinced that they exceeded their quota on that day, as it's more likely that it's a global"ish" issue with a certain group of hosting providers.
We went with the folder permission changes "777" and added lines to .htaccess ... which seemed to help with the "ghosting" other accounts, but still a random problem exists with sessions, more so on IE/Edge, where Chrome brought most success of "normal phpbb operations". However, just this morning, it seems like the "ghosting" has partially returned, OH JOY!!!!
Never mind, we fully intend to have new hosting in a month or so!
All the best,