'Convert to Mono' Results in Silence

[Write In at JNSA]

I'm using Audition 2020 on a Mac. My Zoom H5 records in stereo, so when I import voice tracks for podcasts, I need to convert those to mono. Lately, converting results in silence. In the mastering workspace you can see a noise floor, but it's otherwise totally gone. I can split the channels into two tracks, but merging them (convert to mono) doesn't work. What gives? I've reformatted my SD card, no change. 

btw - I do not have spectral display open when this happens. I'm in the classic workspace.

[SteveG_AudioMasters_]

Without you posting a bit of the file I can't tell - but this is what you'd get if you had an inverted signal on one side of the stereo to the other and they were both identical apart from the polarity. But why that should happen isn't quite clear because they shouldn't be identical... how are you doing the conversion?

[Write In at JNSA]

I added a sample of the audio before and after conversion (disproportionately is the converted blank, so to speak; theppltypically.wav is a sample of the original stereo file). I'm in the audio editor window and using favorites/convert to mono and I've also tried exporting and telling it to export from stereo to mono.

If the signal was inverted, how would I resolve it?

[SteveG_AudioMasters_]

At the RHS of the waveform, there's an L and an R in a box. If you click on one of them (doesn't matter which in this instance) it will mute that channel. If you now go to Effects>Invert it will invert just the highlighted channel and leave the muted one alone. After you've done this, then unmute the channel you muted.

If it suddenly works correctly, then this is what it is - a cancellation caused by two signals, identical in everything but polarity, being mixed together. If this makes no difference though, I really want to see a bit of that file...