I've noticed recently in our development environment that saving a page within a unit can be very slow, taking a minute or two to reload the page. Once this happens, the entire site won't load, although I can navigate with normal speed to other sites on the multisite network. As far as I can tell, everything else works fine.
Here are the specific steps:
-- Admin side
-- Courses > Select Course > Units
-- Within a unit, update a page > Save.
Quick note that I have disabled all other plugins aside from the WPMU DEV Dashboard plugin and we're still seeing this behavior.
On the server side, I've noticed that the MySQL memory usage shoots up on this action and I have measured that with vstat if that would be helpful.
Let me know if there are further things that I can do to help in diagnosing. I am enabling support access to our dev server. I am specifically seeing this in "Test Site 2".