Tested the latest Doctor Who episode (which is upscaled from 1080p) and no stutter anymore Enabled subtitles > I get stutter again, went back into Plex settings > Video > Burn subtitles and selected 'Always' and the stutter is gone! Started fiddling with the settings (Plex app on the TV) and set all qualities to Original for remote too, for some reason it was passing through the internet rather than through my local network so set all qualities to 'Original' to bypass that. Plex is now massively stuttering, also with the Xbox, I knew it couldn't be the network because it is wired through homeplug and tested to be stable at 26/Mbps - 11Mbps up. So my new 43' 4K Samsung 6000 series (2016) TV is here, all great and everything, tried Plex with it and it seemed to stutter a bit (not a lot) but I also got this (ONKYO HT-S5805) delivered yesterday and I set it up today using the HDMI pass-through on the receiver, mainly because it will pass 4K to each HDMI port, whereas in the Samsung TV, the Xbox One S must be connected to HDMI 1 to fully utilize 4K (UHD) - not any other port on the TV (there are 3).

Samsung tv plex app