Error - The resource you are looking for has been removed, had its name changed, or is temporarily unavailable

Good day all.  This error comes up every now and then, but has happened several times this week.  I have seen it trying to add a Method, the main form would not display.  One of my users had the problem with trying to access a custom ItemType (main form again), but I did not have the problem.  We were in a Skype call at the time and the user was sharing their screen, so we were looking at the same entry at the same time.  Last night a user said that they were receiving the error when trying to log in.  I had the user clear their cache and they could get in.  Does anyone know why this happens?  When I was looking through the forums, everything seemed to be from 2016 or older and didn't really have any answers.  We are using v11 SP10.  Thank you for the help.