Hey I have definitely been in that situation where I was invited for an interview and didn't get in. Only because I spent so much money on hotels and plane tickets. Once I followed up and wondered why I received a rejection, those schools also took forever as well. They didn't comment anything about my interview skills, they just looked back onto my application and blamed my grades or GRE score. Which was very frustrating because they had that information to begin with, so I wasn't sure why they even offered me an interview.
But to comment on the group physical part of the interview, looking back I think we just think too much into the interview that we end up making some mistakes. If you would have observed the two male students instead of the females I think it would have been fine. At then end I think they were just trying to observe you and your interaction with the students. Because you chose the females I think that just made you uncomfortable and your reactions could have been interpreted differently by the admissions committee. You were nervous or uncomfortable but they may have taken that as you being uninterested during that part of the interview.
Maynard, if this is your passion I definitely advise you to keep pursuing. I know this can be frustrating because your stats are pretty solid. Maybe try to gain healthcare exposure in a different setting. Volunteer or work, do whichever your schedule allows you to do. Switch up your recommendations if you feel that this might be an issue. But for Mercer, the one thing I do know is that if you're offered an interview, you have met or exceeded all if their requirements to get into their program. They just want to know if you will be a good fit for their particular program. They really praise their students for engaging in team work because once you're in, there's no more competing allowed. Hope this advice helps!