If there are problems with a database’s backup process one possibility is that the Backup preferences file has become corrupted. If nothing else is working and the 4D backup is not performing as expected try deleting the Backup preferences file.
The backup preferences for 4D are stored in the "Preferences" folder that is at the same level as the database structure file. Inside that Preferences folder is a Backup folder, and inside that is a Backup.xml file. Deleting this file will reset the Backup Preferences to default, so if this route is taken it is important to reset any automatic backup settings the database previously had.
Additionally, resetting the backup preferences in this manner will restart the backup numbering process, so the next time the database backs up the file will be name databasename.4bk. It is important to be cautious in this case because previous backups might be overwritten.