Did you guys check for orphaned or duplicate entries (stuck mountpoints) in the /Volumes/ directory, which may cause the mismatches mentioned?
When macOS/OS X tries to mount a .dmg (or any drive) it does it by default with creating a directory in /Volumes and then mounting it to that point (so a drive gets accessible at /Volumes/NAME_OF_DISK_OR_DMG).
Sometimes it happens that the /Volumes/ directory includes (duplicate) directories or left overs, even if the originating drive or dmg has been successfully unmounted in the meanwhile, leading to situations where (inaccessible) ghost drives or wrongly named drives appear when remounting.
The Volumes directory then may include several orphaned directories (/Volumes/NAME_OF_DMG, /Volumes/NAME_OF_DMG-1, /Volumes/NAME_OF_DMG-2, r other strangely named entries or unknown drive names etc.)
To get rid of these (if existing):
- Verify all drives and dmg have been unmounted (check with 'diskutil list' or the disk utility to be sure).
- Check the contents of /Volumes/ e.g. with 'ls -laF /Volumes'. There should only be one here with the name of your startup disk (/Volumes/NAME_OF_STARTUP_DISK )
- Delete the remaining (orphaned) directories 'sudo rm -rf ORPHANED_DIR'.
(As always, the necessary disclaimer to use a sudo rm -rf with all your caution!)