One thing you can try is to find the app, long press on app, next click storage then clear data/cache, close it, restart phone try again to setup.
If your mobile device is rooted or is running a custom ROM, then Secure Folder automatically locks to prevent unauthorized access. If this occurs, you can no longer access data inside Secure Folder.
Worst case scenario is a full factory data reset and not restore ANY BACKUPS and setup as new device UNTIL SECURE FOLDER WORKS, then restore apps if desired.
I hope this bit of info helps in any way.