You would need to make the export permanent. It still would be good to see the logs NextPVR shouldn't be crashing when ffmpeg and ffprobe aren't found.
You will need to enable verbose logging to capture what might be the issue. On the Settings screen hold the key (I'm sorry I don't know the correct one on a mac keybboard) try Command, Alt, or Control and click and it should show a hidden button to turn on the option.