Some traditional games play fine without issue. However, other games (all Arkanoid games for example) simply present a blank screen and never play. I also noticed when I cancel out of this game all other games experience the same issue. Eventually, I found these games cause a loop in the transcoder exe I mentioned in the subject. If I kill this task I can attempt other games but this task will loop unless i take action. Very recreatable.
All games play fine with traditional MAME.
I am running the latest build of Windows 10 pro (19042.844) and the latest Plex (upgraded today 1.21.4.4079) I had this issue when this service was first released but decided to wait a few builds before reporting it.