TT changes my refund amount if I claim my son as a dependent vs. claiming my daughter as a dependent...why?

So according to a court order my ex and I have, I am to claim my son (who is currently 12) every year until he is 18 and my ex is to claim my daughter every year until my son is 18, and then I claim my daughter (who is currently 10) the first year and my ex claims her the second year.  So for 2023TY my ex screws up and claims my son and files her return before I did.  I efile my return, and it is of course rejected b/c we have both claimed my son on our returns.  The simple thing to do is for me to claim my daughter this year on my taxes, however, when I go to do that, my refund is REDUCED BY $100 just by changing from my son as the dependent to my daughter.  

This makes absolutely no sense to me, and I'm wondering if it is a glitch in TT.  I even tried changing the birthdates of the two around just to see if that had something to do with it for some odd reason...it did not.  This is absolutely stupid...I can't figure out why there should or would be a $100 difference in my return just by changing which child I take as the dependent.  Please advise.