@Damoeire the difference between those two keywords is that open will open the item, find will reveal it in finder. For most other types of files, the consequence is more obvious, but with folders, both will end up in Finder. The open command will open Finder to within the selected folder, the find command will select that folder in Finder.
I haven't experienced any issues with either of these keywords and folders, and the actual behaviour of this is controlled by macOS itself (Alfred doesn't do anything differently when asking to open a file or a folder, just passes off to macOS).
Have you tried just restarting your Mac in case macOS is having a funny moment?
Cheers,
Andrew