ok… that’s not good but it shows there’s no particular issue with trailers. your trouble is with local media assets in general.
before getting more drastic 
can you do me one last favor and check if a Plex Dance will resolve the current situation?
- move the library folder’s content to some place not monitored by the Plex Media Server
- scan the library files and wait for it to complete
- empty trash and clean bundles
- move the files back into the library folder
- scan the library files again
–
considering you’re using a test library you could also delete that library and create it from scratch.
does that show the trailers and extras?
If it doesn’t… please go to Settings > Manage > Troubleshooting, click Download Logs and upload the resulting zip-file here (or send it as a DM if you prefer that).
