Problem:
Ally on Canvas removes image descriptions when you fix contrast issues.
For example, here is a screenshot of an Ally error message I would get:

The image has contrast issues. When I fix the contrast issues and re-upload, Canvas removes the image description, which makes it think I have made the image less accessible. It subsequently kicks me off the page, requiring me to go find the file on Ally again and click back in to add an image description.

This is quite irksome. My recommendation would be for Canvas to recognize that the new file that is uploaded should keep the image description of the one being replaced.