Just got my new Ultra and can only get it to display 1080p on my old LG 55UB8200 4kTV. I tried the auto-detect setup and the Roku does think the TV can support 4k, but when it tries to switch, I just get black screen/no signal. Same thing if I try to set the display type through the menu - Roku says TV supports 4k/HDCP2.2/etc. then when I switch to it, nothing. I didn't find anything in the TV settings that would help modify any HDMI settings, so am I stuck using 1080p?
On the back of the TV, the one HDCP 2.2 port is labeled and that's the one I am using. After doing a little more googling, it may have something to do with the Roku not supporting the 8-bit color depth?? Anyway, I solved the problem by ordering a new TV. It should be here this afternoon. Not the cheapest option, but it was time for an size upgrade too. Thanks for the reply,