Well, this is incredibly silly...
It really was just a missing TXI.
I swapped out the texture for a completely invisible one as Fallen Guardian suggested, and of course that made everything visible again. However, anything less than completely invisible would bring the problem back; this led me to conclude it must be a TXI issue, and so here we are.
Now, I noticed that source of this window texture is from Dantooine. I want to make sure changing it doesn't adversely affect anything anywhere else... but I don't remember any windows on Dantooine. Anybody know where it's from?