USB Mountr "Couldn't get root access"

Device OS and version: Lineage OS Android 7.1.2
Device model/manufacturer: Samsung Galaxy Note 3
F-Droid version (in the About screen): 1.2.2
F-Droid privileged extension version (if installed): N/A

What did you do? (clear steps if possible)

Installed software. Restarted device. Ran software

What did you expect to see? Device storage accessible as a usb memory stick

What did you see instead? Message "Couldn't get root access"

The device is rooted

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information