I've had a report from a student that all the changes that they had made to one of the files for their assessment were lost, with the file reverting to that originally distributed. This was reported to me at around 1800 GMT yesterday. Project link is here:
Since this is for an assessment the student has since been recreating the lost work, so the file has now been updated.
The student reported that they had been saving the file as they went along (this sometimes doesn't mean they actually pressed save, since it's quite common for the students to assume that the file is saving automatically as it's usually still there when they close the browser and come back to it later!), then left it for a while; when they reopened the project, the work they had done was gone.
I had a couple of similar reports from other students a few weeks ago, which I can dig out details for - this is just the most recent one.