I use HDMI port 2 and don't have problems with it (yet). I'm going to guess you have the enhanced mode turned ON.
I don't have a spare 18gbps cable to test, but the HDMI2 port seems to be resulting in intermittent signal drop. Has anybody had that happen other than me on one of their ports, whether on this TV or others? Basically the signal from my PC occasionally drops for about half a second then the TV picks it up again. It hasn't happened since I switched to HDMI3/ARC.
Additionally, does anybody else notice that the top right and top left corners are occasionally slightly dimmer/duller than everything else? I notice it a lot with web browser usage, and I wasn't sure if that was specific to my TV or whether it's the nature of the local dimming.
Does it happen with 1080p and 4K?
Yes i also notice that on the top corners, the picture is slightly duller.