Seems to be a problem with 4.8.4.0 since everything I scanned in this morning after updating seems to be having issues (including media that previously scanned in successfully so I don't think it's a problem with the files necessarily). For this example in the log, I scanned a show folder back in that I previously moved out of the library, and tried playing an episode.
Playback Error...
No Audio/Subtitle Selections...
Server Log...
embyserver