I would ask for further detail on what was done to resolve the error and keep asking until you get an answer that makes sense
The answer does not make sense to me. What I am saying is- it sounds like something from the server was causing the course to cache but what that would have to do with hide and unhide ...
I know you have a huige moodle site so if some tweek to help your load times had this affect you should get that information documented.