Same issue here, there is a workaround:
- Install Kodi on your Xbox One
- Launch Kodi, goto addons; search for Plex and install Plex
- Run Plex Addon
- In Plex settings enable X265
- In Plex settings set remote quality to original
- Set Plex addon to run at Kodi startup.
When you startup Kodi Plex will run from Kodi and the problems are gone …
