I have a 2014 model 4K Samsung and I am having the same issues. I originally set it up using a DECA converter, but when I mounted the TV on the wall a day or 2 later I ran CAT5E to my router. 90% of the time it is great, other than it being slow, but I can live with that versus having a box. I am also getting the stuttering issue that corrects when you change the channel. It seems to happen more on some channels than others, and more at different times of the day. I had to use a cable box for the superbowl, it was really bad. I can watch TV all morning with not a single issue, my wife comes home and wants to watch DR. Phil and it starts. I do not like him, so I am ok with it! Since it was plugged into my whole house router, and it would start after a certain time, I thought maybe the ****** Linksys router was broadcasting internet traffic more after kids were getting home from school. Yesterday, I purchased a managed 5 port Gigabit switch, set static IP addresses, and only have the samsung TV and the DECA from the main splitter connected to it. I am still having the issues, so there is no way it is network traffic.
I don't think it will make a difference, but I am going to try using the DECA again, just because if I call tech support they will ask.
If anyone has figured out why this happens, I would love to know.