I've noticed all of these 'empty' trailers are a 4.92mb video file that runs for a min or so - just a black screen with the message 'this trailer is not available from this app. Go see Youtube.'
All of these are trailers with '[HQ]' in the name.
I'm getting around 30 or so apparently random trailers downloaded per night of these, despite my config set to download HD only.
When I enable TMDb on the Search Providers tab of Trailers plugin I get the trailers from TMDb but when I try to play them the playback jitters. Manual search using OnlineVideos with YouTube works as a fallback.