Thanks for the posts, Mike.
I think I understand what you're saying...see if you agree. With streaming content, the resolution changes as bandwidth changes/stabilizes. The stream may start out at 480, then bump to 1080 or 2160 if bandwidth allows. It's at those changes in resolution that you feel may be causing issues? By forcing the device into a resolution, you remove those transitions. Higher end devices like the Shield upscale, so there's no changes in the resolution as far as the screen/tv is concerned.
I'll try forcing the Roku.
Exactly. Changing resolutions is problematic with a lot of home theater equipment as well. My home theater processor will occasionally act funny when switching between 4k and hd content on netflix. It seems like this may be the problem since the blu ray which is fixed 1080p worked without issue.