UK freeview HD playback issues on HDhomerun

Hi
im moving from Windows MCE to Plex for live tv and recording, using 2 amazon fire TV 4k on the LAN, and cannot playback live tv or recorded tv at full quality on the amazon fire tv i have to transcode to 720p,
when playing 1080i (i think) the screen is paused but playback of the audio carries on in background . reduce to 720p and its ok, i thought a firetv should be able to play this as it can play back ripped blueray no problem
its not an issue with the plex as it shows throttled on playback, also the units are on 1 gb lan i have tried them on wifi (ubiquiti AC) and still the same issue

anyone else with the same issue?

Similar to this: https://forums.plex.tv/discussion/284669/shield-tv-and-plex-web-app-cannot-playback-this-recording-3-issues-found

it looks the like the same issue i will post on that thread