In the previous Plex version on Xbox One, movie playback would pause (for buffering purposes) maybe once out of every 6 movies or so. Maybe this was caused by temporary network issues. In the current version, it happens at least once or twice with every movie. On top of this, occasionally the movie will stop playing entirely and give the message "An unknown error occurred" or "There was an error decoding". When I resume playing, it starts playing again with no issues (until the next time it stops).
Last night, my wife and I tried to watch a movie and it would error out every 1:20 minutes or so. The only way I could get it to play through was to reduce the local quality from "Original" to "720p 2 Mbps" which was not very enjoyable. Video and audio quality took a nosedive from the original 1080p quality but it was the only way to actually watch the film.
I never had this problem with the old version, and the Plex app on my $20 Roku box works fine.