This issue has occurred twice to my team recently on 8.3.8 and it caused a ruckus, so wanted to make the devs aware.
If you create a perspective folder with a random name, move your files into it, then relabel the folder name to one of the file names that used to be in that folder, then save. If you then follow that with a gateway backup, the gateway backup version confuses the folder for a file, thus showing it as a file and acts as if it is corrupted if you try to open it.
I fixed it in both cases, by exporting the corrupted file/folder, unzipping it, moving the export files to a new location to remove the conflict, zip the files, then re-importing it.