Video Export quits without doing anything

The video export feature has worked for me the whole time, but now one session is giving me issues. When I click Export Video, the progress bar shows up really quickly and then just vanishes. No output file is produced.

I tried to open the same video file in a new session and export a test there (using the same pathname): it works. So it’s not the video file or the path.

The audio mixdown by itself works fine in the problem session.

So the question is: what’s there left to try? This is kind of weird, because basically both features work in isolation. So what can be different about the session?

The only thing I can think of is that the problem session has a 5.1 output as Main Mix, with the stereo output used for video demos being a secondary output. The other session that works fine has a stereo output as Main Mix. But at least assigning the secondary output to be Main Mix didn’t fix this, so it doesn’t seem like that’s it.

Other than that, I’m all out of ideas and back to using my custom Python/ffmpeg script that I used for video demos before this feature! But would love to keep using it if I could just figure out what’s causing this issue. Anyone had similar problems?

Same problem both with Nuendo 10.2.20 and 10.3.