XPS 13 Plus will not go beyond 1080p on ONE of my external displays

Just got my new XPS 13 but I have the weirdest issue that I cannot resolve, and am trying to avoid returning the laptop to dell for a refund. 

I have two external displays. Both 4k. One is an LG c2 oled, and the other a gigabyte m32u. 

The gigabyte m32u which has a dedicated type-c input works fine. 4k and 144hz. 

but the dell refuses to output more than 1080p to the LG tv, no matter what I do. 

I'm using an 8k capable type-c to HDMI 2.1 adapter (in fact, I've tried two). 

Both of the adapters I've tried will work no issue with other devices. So my macbook for example does 4k no problem via the same adapter. 

But the dell, not matter what I do, will not output more than 1080p. 

Weirdly, the intel graphics control panel is detecting the LG TV. Reports it's capable of 4k. displays the correct edid data showing 4k 120hz as a supported resolution, but the control panel still tops out at 1080p. 

I've tried adding 3840x2160 as a custom resolution, and it even seems to think it's working. It lets me select it, and doesn't show any errors. But i'm still in 1080p. 

I use the LG TV as a monitor for my work, and so if I can't fix this issue, I'll need to send the laptop back to dell. 

Does anyone have any potential solutions?