never seen that before (not here in the forum nor in the official FS-forum) and I can´t say what it mean … the question is, what else do you have installed, or do you use any addon-linker programs, …
I can´t really believe, that this is only due the navdata update. When you remove the navdata cycle, all looks good? Happens this generally, means on all airports?
Thanks for your suggestions. As it turned out the issue was due to an old version of the Working Title mod for G3X. The upside Y went away when I removed the Navigraph data, but there were other issues that I was not aware of at first like a black background on the glass screens.
Updating all of the Working Title mods seems to have fixed the problem.