Hi, and welcome!
We've grown so used to SAAS just working that it's easy to forget that RStudio Cloud is still in \beta. I'm reliably informed by RStudio staff that the cloud team monitors here for issues, and recently there seems to have been a raft of them. From what I've seen, the solution usually entails killing the host process and re-spawning it. I've heard some reports of data thought to be lost reappearing, but I don't have any idea as to whether that is universal.
Also from what I've seen, usually the associated project id is needed for the rescue process, which makes sense because it discloses less than an email address.
I am fairly sure that there is nothing on the user end that can be done for this problem. A good practice if Chromebook flavored OS supports it would be to compose and save on RStudio Desktop for copying into cloud, so that a minimum of work is lost if this happens.
Whenever a coding issue comes up, please encourage your students to see the FAQ: What's a reproducible example (`reprex`) and how do I do one? Using a reprex, complete with representative data will attract quicker and more answers.
Also, of course, the homework policy.