XboxOne and PS4 plex grainy video issues

I put this on the general area because it’s happening on multiple OS’s.
I am running the latest plex server on the latest unraid 6.2.4 (though this has been going on for months).
Everything that I’m using is in the original quality. I have tested old and new and various types of video files. It seems to all be the same.
All of my problems are via a wired ethernet connection from either my xbox one or my PS4.

The problem is this: The video is grainy or pixelated on both platforms. For the layman it’s still watchable. But when I switch to ANY other platform there is a dramatic quality difference.
The video never buffers…yet sometimes it might skip a second or the video suddenly becomes mushy or blurry and then snaps back to normal.

My iPhone 7plus, 6plus, 5s and 7 Plex apps do not have this problem.
My amazon fire app does not have this problem.
My Apple TV app does not have this problem.
My Samsung TV app does not have this problem.
Nor does running it off of any browser from my MacBook Pro have this problem.

If I should be posting this on both of the platforms that I"m having issues with, please let me know. I’ve never really posted on here and I just want to figure this out, if possible.

Thanks for the response, trumpy. I suppose this is possible…but it doesn’t explain why this seems to happen on the xbox one and ps4 but not on any other device I’ve used. As for the file being of ‘marginal quality’ that might be the case but seems odd that so many files from various shows would all be of ‘marginal quality’ that play fine on other platforms.

That said, I’m thinking it was a software issue…because I’m not noticing it as much now…watching the same files. It’s possible an update has fixed the issue. I’ll keep an eye on it.

Thanks again.