There are a couple of scenarios where this situation is seen. Both begin with the teacher intending to use letter grades, and because of it, initially specifying no points. This “no points initially” is key to what happens below. We understand that this is an expected behavior, but would like to see at least a warning message before the change takes place.
One scenario occurs when a faculty enters letter grades in the gradebook manually then changes to using a points-based grading scheme. After a save, all the grades are wiped out and replaced with 0. There is no undo and all the entered grades are lost. (example video: https://goo.gl/fP1wjx)
A second scenario with similar results happens when you start with letter grades and decide to edit points from 0 to, say, 50. After a save, all the grades are wiped out and replaced with F. There is no undo and all the entered grades are lost. (example video: https://goo.gl/FBbDAv)
Because of the severity of the consequences, we would like to see Canvas include a warning message before wiping out all non-conforming grades. Since the current functionality works as Canvas intends, it is not categorized as a bug, and we would like to ask the community to support our request for a warning message to be displayed.