What sort of mics?
Positioned how far from the people speaking?
Did you listen to each microphone as a single mic or were you listening to the mix of both mics?
Did you mix to mono on site or recorded them as separate tracks and then mono’d them in post prod?
Have you ever tested your mic cable wiring are they correct ie; pin 1 to pin 1, pin 2 to pin 2, and pin 3 to pin 3?
Are they pro made cables or DIY cables?
Any or some of these could be the problem……
My gut feeling is it a 180deg phase problem, if you still have the recording as 2 separate tracks phase reverse just one track (either one … ) then try to mono mix it and see if that makes a difference.