Do you mean a CRYPTOMATOR_RECOVERY folder?
If yes, then there should be all files and folders in there that are “orphan” thus whose directory chain could not be resolved any more and would mean that you have not seen these folders in the vault any more.
The problem with files in this CRYPTOMATOR_RECOVERY folder, however, is that we can’t recover the filenames and file endings because of the file name encryption. We have a script here that can recover most of the file extensions but the names are unfortunately not recoverable this way: Sanitizer: Restore Missing File Extensions (Please ignore the section about the Sanitizer, it is now integrated into Cryptomator).
Tomorrow we will publish an article here that describes the background of this case better, i.e. what is an orphan directory, why can they occur at all, how do I recognize them (health check), how can I repair them again?