Still not sure what's the issue but it has to be something rather simple, problem is to nail down what's wrong.
At this point I would try the followings :
- Completely uninstall VLC ( might be worth to check on their site if there's a manual uninstall guide )
Reason for doing this is files association, and you can always reinstall it afterwards if needed.
- Check if you are using Core Audio as the default audio driver on your Mac.
Sometime after installing other apps, there are drivers and audio daemons getting installed, you may want to check if you haven't got anything new or weird in those path and delete them and reboot your Mac.
/Library/Audio/Plug-Ins/HAL ( to check the installed Audio Drivers )
/Library/LaunchDaemons ( if you remove a driver from the previous path, there might be a matching launch daemon to delete as well, otherwise it will run again after rebooting ).
We are talking Main MacOS Library path here, not the User Library.
Check your Hard Drive format via Disk Utility and info and make sure you haven't a Volume Type with "Case Sensitive"
Then the last option would be to reset your Mac from the Recovery partition or Time Machine, recovery on Mojave should keep your personal files.
The section about resetting Core Audio might be one to try.