I imported an assignment for my class. It merged or replaced another assignment and I did not realize it at first. I deleted it. This was where it got weird. It had the title and text box of the second assignment I imported, but the student submissions are all there and are about the other assignment. These were not similar at all. I tried Undelete. I am trying to find out where the second assignment went or why it "replaced" the first.
Did you import the assignment using the Course Import Tool? Or did you use the copy to option to add the assignment to your course? If the second, according to How do I copy an assignment to another course?, "If you copy the same assignment to the same course more than once, the assignment you previously copied will be overwritten with the newly copied assignment." If you did use the copy to option, that could explain why the first assignment's instructions were overwritten with the same instructions as the newly copied assignment and still display students' submissions that were based on the old instructions. As far as reverting changes goes, I'm not personally aware of a way to revert these types of changes, but you could always reach out to Canvas Support to see if there is a way to do that.