XBox One issues with LG TV

LG's HDMI support is notoriously unstable, not sure if it is the way they handshake or whether their software is poor but it is a long standing complaint you can find in many places on the internet.

Xbox 360 had issues with LG TV's as well (do a web search for xbox one lg tv hdmi and you'll get pages of results including PlayStation issues connecting to LG TV's so not limited to Microsoft).

Things to try:

On your TV that it works with, set your Xbox One to a lower resolution i.e. 720p then plug it in to the LG TV and see if it works.

Check for a TV firmware update

Reset TV to factory default settings

Try other HDMI cables

Try a HDMI to AV converter for your sister's TV and use AV cables with your Xbox One when using that TV.

I have the same issue with Xbox One X and LG 55E6V TV

As I said, it's an incompatibility between the Xbox and TV hardware. I understand it's not happening with other devices but as explained above the issue is with the TV and LG would likely have to replace specific hardware to fix this issue. The fact that other Xbox users are having issues with LG TVs (but not other TVs) reinforces this further, LG will need to address this on their end.

Thanks,
Kyle

I have the same exact issue, with the same LG C7 tv and Xbox One X.

I am having this same issue with my Xbox One X Scorpio on my LG OLED TV.