when C4D crashes, the files witch are opened are automatically saved in the bugreports folder.
With the v3, the file can’t be opened, it says : structure de fichier incorrect in french.
Before v3 C4D usually saved a recoverable file.
As Imran has mantioned, unless this was caused by Corona there’s not much we can do. Contacting Maxon would be the option here. If it was Corona related, then sending us the bugreport and a minidump to our private uploader (link in my signature below) would be good.