I have run into a problem where the file association for a packaged file created by our app is not properly associated with our app on macOS Sierra 10.12.5. It is only happening for a single customer and there definitely seems to be a problem with maintaining file associations on their system.
For this particular app, files created by the app appear as a directory instead of a single file in Finder, so trying to manually associate the file through the Get Info panel is not available.
I know you used to be able to find and manually manage the file associations in com.apple.LaunchServices.plist, but this does not seem to exist in Sierra. Does anyone know how to list the file associations in Sierra or manually add an association for a packaged file on Sierra?