I'm sorry it's been so frustrating. Yes, that would be helpful to submit a bug report, because it will help us to track the follow up that we might need, and definitely if it happens again. Also, if you submit a ticket, we can potentially log in as that student and see whether there's anything we can find.
I had a student with a similar issue, and eventually I realized that she had somehow clicked "Remix" and was not working in the right place anymore. Her new code was in her "Projects" area instead of the course workspace. As a teacher, you can check to see whether this is the case by clicking on the name of the course in your teacher dashboard, then choosing the "Projects" tab to see all of the projects from your students.
The student can also check by clicking "Projects" on the top of the screen in Code Studio.
Thanks for your patience on this. I know from experience how it feels to see your students work hard and lose all the things they're so proud of.