Missing disk space on macOS
It seems like the two most likely candidates are a mounted (shared) disk overwriting a location with large files, hiding them from your view, or large (or many many small) files that are held open by a process, but have already been deleted. If you haven't rebooted the computer yet, that's worth a shot, but also booting into recovery mode and running first aid on the disk might help. lsof | grep deleted might also reveal interesting information, if lsof is available on OSX (I assume it is, but I've never looked)

I've also noticed in my own use that if I use a tool like DiskInventory or Grand Perspective and there are other users on the system, they won't show the size of other users files if I don't have read access to them (reasonably so). If you have other users on your system, they may have large files in their home directory you're not seeing.