Got a good American server with loads of 4K films. Got 45mb internet connected by ethernet and they are stop start stop start. And some fail to play. I have a 4K tv and a tx3 mini whisk says plays 4K which I’m doubting
i installed the same box on a friends broadband played some vod, picture was amazing he has samsung 4k tv wasnt even a 4k stream but it upscaled the picture so sounds like it could be your provider you need 25meg for 4k which you have easily, try on youtube theres 4k demos if it runs them its the server, If its still stop start then its your internet. Your internet service provider could be choking your bandwidth virmin m do this a lot.