Thank you very much. The problem has been solved, and I've found the cause. I'm an "application developer" myself; both plugins use FFMPEG, and I suspect that they're somehow interfering. Both probably gained access to the output file and blocked each other, which is why the file was ultimately empty and blocked. This kind of thing should obviously be fixed, because it's difficult to debug when unknown installations are messing around in the background. I was lucky that I figured it out on my own because I had the same problem with one of my own applications.
Have a nice trip and don't overcharge the company. 😁