To summarize that post, in case it gets lost some day, the author said that ViaCAD stores the location of dialog boxes in a ".ini" file located here (in Windows):
And by renaming or deleting that file, it will force the program to create a new one, so any corrupted stuff will be wiped away. It turns out that is what fixed my weird issue, since it was the export dialog box that was not showing up. I suspect it had to do with the recent installation of a 3rd monitor in my setup. I have observed strange dialog box behavior with ViaCAD in the past when using multiple monitors, so in hindsight this makes sense. When I went to look at the contents of the old (broken) file, in the export category it had the following location:
vs the newly generated file, which has this (and this one works):
So it seems that the dialog box was popping up off screen, as the X value was negative. Possibly moving the monitors around, or swapping the primary monitor would have allowed me to see it. In any case, I'm really happy removing/renaming the .ini file worked, since I was about to re-image my PC, and that would have been a bit of work.