This is a new one, and I can't find anything about it.
(self hosted) Students are complaining that they can't see images on course pages. I can replicate the problem in Student view - images that are visible as a teacher or an admin return a 401 as a student.
As it turns out, the teacher had inserted a link to an image _preview_ instead of properly inserting the image itself. This stopped working with a recent update.
There's no help needed, but I wanted to report it in case someone else runs into it.
--Jorge