So I partially solved it--for some reason the software produces the files much slower than it used to. The 2.5 MB stl file I was using was too big for it to ever finish, but when I use a 100 KB stl it manages to export a .x3g. However, I've used 15+ MB stl files in the past and had no problem. Does anyone know why there would be a sudden change like this? I recently updated to v3.3 so maybe someone else saw a similar change when updating their software?