When using the dropdown menu to flip between question bank category in my courses, I receive an error: Exception - sessionwaiterr. (See image below.)

This happens when I'm flipping to a category that contains questions currently in use in a Quiz. I'm entirely unable to access the questions in the category.

Instead of being able to flip to the question bank category, I receive either a 504 Gateway timeout. Or the "sessionwaiterr" error message.

The entire site then shuts down for 5 - 10 minutes until I can reload again.