Nuendo 4 -Stereo Export Problem

Hey guys,

Ive been using N4 forever and I recently switch my intergace from RME to UA Apollo. I assigned my drivers and buses, but when I try to export an “existing” song to a single stereo file, it is not in stereo.

I try a new song from scratch with some basic tracks, and exporting to a songle stereo file workes fine. (I panned a few tracks hard right/left, and it was fine.

Back to othe existing songs in the works, I cannot mix them down in “stereo,” without clicking on “split tracks.”
Its strange I made sure the vst connections are all correct in my device setup and cant figure this out?

Anyone have any suggestions?

I can only think it has something to do with switching interfaces on an existing song? Any help appreciated.