The dx could be the issue. I've had times where the internist sees the patient, then refers to specialist in same group, same day, same dx - the insurance denies first go around, but on appeal it gets paid. (most of the time) I think some of the insurance's claims processing edits automatically denies if same dx, multiple docs without regard to specialty. In hopes you write it off and forget about it i'm sure! LOL. In a multispecialty group though, you should have less issues getting paid- as long as too though, the credentialing & specialties are set up correctly! If different dx's it shouldn't be a problem, should be paid first time. And also- you could have two doc's with the same specialty see the patient, same day, but one has an area of expertise in the field...these will be paid on an appeal basis.
Good luck