Audio from Video not importing. Video only imports, after modifying 5.1 audio tracks

I'm working on a project that has video clips with 5.1 audio. In order to isolate the dialogue track, I modified the audio channels to mono tracks.

Then, I handed the project off to another editor who needed to relink the media. He relinked it to the original video (with 5.1 audio), but now there is no audio. It deleted all the isolated dialogue tracks.

And now, when we try to reimport the original file with the 5.1 audio, no audio will import. It just imports video only. I even tried on a compeltely separate computer, and it's still happening. This is super weird. Any help here???