Thanks to everyone for the replies. I was not aware that there was a WT mod for the G3X, I can see from my Community folder that I installed the “workingtitle-gx” mod two days ago, apparently when I installed the VL-3 mod. I’ll update all of the WT mods to see if that helps.
It’s funny that I didn’t see the problem until after the Navigraph data update, and that removing that got rid of the Y, but I see now that although the Y is gone, my G1000 screens are both black. That was the case before, but I didn’t see it due to only seeing the big ugly Y.