I have the above mentioned 55 inch smart TV which I bought new recently.I upgraded from a similar specced rented 49inch Samsung set. I had my PC connected to the old set via HDMI as a monitor while I'm editing video,and it played everything I could give it without any problems.Even high bitrate (100mbps) 4K videos weren't a problem for it. The same can't be said for the new one though.Not a single thing has changed at the other end of the HDMI cable.The PC and Nvidia GPU settings are the same,and I'm still using the same HDMI cable that gave perfect results with the old set. Any video with any real movement in it gives a horizontal line across the middle of the screen that causes slight but random left and right movements above and below the line.If the movement in the video slows down,the line and flickering isn't there any more,the same if still images are showing or if you pause the video. If I watch the same video from a USB flash drive,it plays perfectly without the flickering.The set is on the latest firmware update,is there a hidden setting somewhere that might need to be changed to stop this?