Does an external handheld microphone affect audio rendering in Premiere Pro?

Hey,

I am recording short promo vids for an event and I have just started using a handheld microphone attached to my camera by cable into the microphone jack for interviews. The audio plays with the video fine in Premiere pro itself and both the audio channels I have checked are stereo. However, when I export the video, only the Adobe stock backing track music is playing in the background and there's no dialogue, but only on some devices. For example, on my device both the dialogue recorded on the handheld microphone works along with the backing track but only the backing track plays on my boss' computer, unless he has headphones plugged in. I've tried the video on multiple different devices and people and it seems entirely random as to whether the dialogue audio will play or not. Audio filmed on the camera's internal mic, i.e not the handheld mic works fine but I'm wondering if this is a new issue because of the new media input channel? 

Hope this makes sense!