you have to not be in edit mode when you export.
I'm aware of this, it wasn't that.
What it may have been was confusion in Blenders internals. What originally caused the issue was joining two objects with different material and texture mappings together to allow me to align some verts using "snap cursor to select" then "snap selection to cursor". After which I separated the two joined objects back into two individual objects. But I forgot to reassign all the materials and they both had picked up the others setting as well as their own. I think even though I finally caught that and reassigned them individually, Blender may have still been confused.
What is interesting though is I did compare the broken landinglightcover_D object with a non-broken version in another .ac and they were identical. I was able to verified it was that object that was indeed causing the trouble, even though it appeared identical in settings to the one that worked.
Obviously there had to be something it was doing in that .ac that the sim didn't like and closing Blender and restarting it, then exporting again, appears to be what fixed this issue.
Thanks for taking a look anyway, I appreciate it.
Kansas and Ohio/Midwest scenery development.
KEQA, 3AU, KRCP Airport Layout
Intel i7/GeForce RTX 2070/Max-Q