I got the same LUD to say cased transferred from TSC to NSC for interview. My 2nd I-485 filed just in 7/2 so it cannot be in the sytem now. Therefore I think interview is not because of two I-485. However, my I-140 approved from NSC, that could be the reason. I'm secondary applicant too based on my wife's EB2 and her case was approved. It looks either you have I-485 or I-140 at NSC this situation would happen for secondary applicant.
I called USCIS, and was told they transfer the case for faster processing. They didn't admit it's a mistake.