The issue is that the plugin you had installed probably activated the debug mode of PHP or Wordpress, and when you deactivate it, you no longer have the error, but if you use the wordpress debug mode as true, you will probably see it againJust click on the link in my previous reply and read my post, all information is contained
I'm only trying to assist and my fix and specific plugin that caused the same PHP errors, might not be the answer for everyone
The Maintenance Page Plugin must have blocked WP Rocket in someway