This bug has been reported to the Roku developer as it only manifests on my Rokus and not on my other devices but I thought that it might be helpful to directly address this on the Shield's forum:
I have been testing my Shield TV's server and I ran into a problem that only shows up on the Rokus, both the Ultra and the Roku 3. My Shield (as a player), My Fire TV and my Raspberry PI do not have the problem.
At first I thought it was the shrunken picture problem that we found on the Ultra earlier as the picture is shrunken in the same way horizontally but, when I switched over to my 3 the problem was also there.
After investigating I found that my regular server (on a Windows 10 computer that cannot use HW acceleration) did not produce the problem and then I looked for differences.
I found that the Shield was using hardware acceleration and my regular server was not.
I turned off that on the Shield and the problem went away I turned it back on and the problem reappeared.
Again this only shows on my Rokus and it shows on all of them. (I have 4 a Roku Ultra, two Roku 3s and a Roku 1)
The problem seems to happen on many, but not all, transcoded videos.
The attached zip file has all my logs plus the XML for a problem file and the Ultra's logs.
To produce the Ultras logs I first turned on HW acceleration on my Shield the I started the Plex app.
Then I played a short part of the problem file and verified the problem Then I stopped Playback.
Then I turned OFF HW accel and started playback again and verified proper playback.
I Then stopped the playback and captured the Ultra's logs.
If this is a problem in the server then it only manifests on my Rokus and if it is a problem with the Rokus then they are somehow treating streams produced by HW accel differently than streams produced regularly.
I hope this can get resolved either on my Rokus or in the Shield's server as I seem to have much better performance if HW acceleration is used on the Shield.
Thanks for looking into the problem.