I have been having a couple of issues with my 4K 60Hz Samsung TV which I am using as a third monitor on my rig.
Here is my set-up:
GPU: XFX RX480 8gb GTR Black Edition
CPU: Ryzen R7 1800X
Motherboard: MSI Carbon X370
Radeon Software Version: 17.12.1
Basically what happens is I set my tv to be displayed @ 4K resolution and it stays that way for a while, then it goes back to 1080p when I turn on my computer. This is a relatively new problem. I've had this set-up since August 2017 and its been working just fine since then. After the resolution changes, I can't change it back. Windows 10 doesn't seem to be able to detect it as a 4K monitor, not giving me the option to set it to that resolution and setting 1080p as the recommended setting. I have a way to temporarily fix it, but its a pain in my a**. The resolution goes back to normal automatically when I reinstall the RX480 graphics drivers. I was thinking that maybe if I set a custom resolution, that might more permanently solve the issue, but I'm not quite sure what I need to fill in for the all fields, so I just left that alone for now.
I'm both open to advise and the info for the custom res @ 4k I would need.