Illustrator did NOT save my progress, even though I manually saved.

Graphic Design student here. I was working on a class assignment on the latest Illustrator version. I was working for about 3 hours. I periodically save my work, probably every 15-20 minutes. I got to a good break point, saved my file, and exited Illustrator. When I reopened the file later, about 90 percent of my progress was GONE. It has reverted to a save point that was only about 15 minutes into my process. 

This is extremely frustrating, as this is probably the 2nd or 3rd time this has happened to me. I've gotten lucky so far that it has not been more than a couple hours of work. But I am concerned that this could happen on an even larger scale! Adobe software is supposed to be industry standard, so why do myself and others keep encountering terrible bugs such as this? Its really quite infuriating. 

If anyone knows a way to recover my progress, I would greatly appreciate your input. So far, I haven't been able to find any solutions, even though I have found other people who encountered the same issue. Adobe, PLEASE fix your buggy software. Thank you.