Dear Plex team…
I just checked on amazon.de a few moments ago and the Plex for FireTV app in the Amazon store is seven releases behind the original Android app accoring to your own release notes.
Here is what I found:
Neueste Aktualisierungen
Was ist neu in Version 6.12.0.3239
WHATS NEW:
[Mobile] New photo details screen.
[Mobile] Playback speed controls for audio player.
[Mobile] Colorize media notifications on Oreo devices.
FIXES:
Timeline/jump letter scroll handle doesn’t change color while focused on Android <= 4.4.
Improve quality in photo player.
[Mobile] App would crash when browsing queue after adding and item using “Play next”.
[Mobile] Moving items up in the recording schedule don’t get them in the right positions.
[Mobile] Show camera roll media setting no longer resets when app is started cold.
[TV] Videos in photo libraries sometimes not working second time they are played.
End of what I found 
The most actual app is: 6.13.6 (with ExoPlayer v2 and a couple of bug fixes). Do you have problems releasing the ExoPlayer v2 update on FireTV? We all know that Amazon uses its own port of ExoPlayer v2…
Updates for the FireTv are posted not as frequently as regular Android devices.
Amazon has a stricter (and longer) approval process for their own devices.
Okay, thank you. I just asked because, normally the delay is less than a week 
The extra delay this time was due to all the hotfixes. The latest version 6.13.6 has been submitted to Amazon for approval so it should be available soon.
Thank you… since Exoplayer v2 … I do have initial jerking of video (not audio) of H264 movies while caching is going on. Later on, this jerking stops while the movie is playing. This happens on my Samsung tablet.
My Moto phone got the 6.13.6 update yesterday from the Google Store.
@rossinior said:
@“MovieFan.Plex” said:
@rossinior said:
Thank you… since Exoplayer v2 … I do have initial jerking of video (not audio) of H264 movies while caching is going on. Later on, this jerking stops while the movie is playing. This happens on my Samsung tablet.
Did you install Plex onto that tablet from the Amazon Appstore? The appstore hasn’t updated yet so you couldn’t have gotten the version with the new player.
No. Google Store…
Ok. Since this has nothing to do with the release on the Amazon Appstore, I would suggest starting a new thread with logs for your playback issue.