Multi Channel to mono works for me as long as the stereo audio is not in musical mode.
If the source audio is in musical mode - even at the same tempo as the tempo track it does not work. It results in two tracks being created with an extremely short piece of audio on both.
If I use sizing applies time stretch on the audio - multi channel to mono does work.
I’m on El Capitan which isn’t officially supported so it may be because I’m not on Sierra / high Sierra
It doesn’t look good at all but this is currently rather a limitation than a bug and it is documented for the Convert Track feature for going the other way:
It is currently not supported for the musical mode.
However, development is collection several issues and limitations regarding split and combine features for future enhancements at the moment.
I never saw the prerequisites in the manual. I’ll just have to work some extra steps with my older projects.
Looking forward to the future enhancements.