I think we traced your issue down to ultimately being that your site needed PHP 7 while the system put you back on 5.6.
That was the issue for our "admin" site. All our client sites had issues with MainWP. Renaming those plugin folders in cPanel File Manager brought the rest of our sites back online. (and I'm pretty sure it was MainWP that required PHP 7 on the admin site.....)
Just trying to help... I would have much preferred being able to fix the issue myself without having to bother you guys.. you got a lot on your plate right now.