Can you screenshot what this looks like? Maybe you can ask Synology since its their apps interface that's saying this. I have not heard of it before.
What happens when you uninstall the DVR in the apps interface? Is it still listed there?
If you enable SSH/SFTP on your NAS you can go into and delete (or rename) this folder:
Your recordings and backups are stored separately in a share, and you can use those to restore after you reinstall the software portion.