At least three times today, as I have been working on a self-guided course (XAM140), one of the pages suddenly disappears, and I see the following message: "The resource you are looking for has been removed, had its name changed, or is temporarily unavailable." I have to go back to the Xamarin U home page, find the class again, start the self-guided course, and find my place in the course. It is a major annoyance.
Has anyone else seen this behavior? Any way to fix it?