Unexpected file format revisited

Something weird just happened, I had 2 files open, making no changes. As I switched between them the “unexpected file format message” message appeared. I also had Layout open at the time. Not saving the other open model, I closed SketchUp. I reopened SU to each file again and found no damage to either. This is running on a local drive with daily backups at night.
So just playing around with both models open, I tried to open one from Trimbal Connect, and the “unexpected file format message” appeared. After closing SU, I then opened the same file from Trimbal Connect with no issues. Strange happenings indeed. This is using the 2024 version.