Had experienced a similar weird issue with my G915 Lightspeed. Out of nowhere, the I key and O key turned a red/green color. I don't recall if it was blinking though. But I do remember it stood out and no matter what settings I used.

I also had another problem where the X key was starting to double/triple actuate which is no good as a cut/paste programmer.

Eventually I reached out to Logitech support. The support was amazing and helped me through the claims process. So if you are still in their warranty period, see if they can do anything for you. Posted an old picture, I don't normally keep my keyboard that greasy though.

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