Envoy is getting more selective because of the flow and I believe it’s nothing about your background checks because i think they don’t get too deep into it before you pass the interview and get the CJO from the captains board.
Mesa is starting to “act like being selective” due to it’s reputation of literally hiring anyone anywhere at anytime. You’re not the first one i see that has been rejected by Mesa recently. I know people who got rejected by Mesa in the last 4 or 5 months and got hired by Republic, Expressjet and Skywest.
So i would say that you’re just unlucky because the first 2 you picked are either being or acting like being selective these days. So there’s absolutely no reason to freak out about it. Just check your app for any mistakes and give other regionals a try.