After you file

I suspect the change has to do with the child/children

Your 1774 + 2426 = 4200

.....and that is likely to have something to do with the child tax credit/advanced credit   ?  3 x 1400 = 4200.

(Edited:  But I'm probably confusing the Advanced child tax credit with the "Additional" Child tax credit...that "Additional" one is $1400 per eligible kid.  I get them all mixed up too.   What is the Additional Child Tax Credit? (intuit.com))

(edited out)

(or could it be you are separated/divorced ..... and there is a conflict as to which ex-spouse is claiming the child tax credits for 2021?)

You may need to carefully check the birthdate(s) of your child/children if you are certain their names SSNs are correct......when entering birthdates, you need to enter the entire 4 digits for the year of birth...not just the last two.

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But no, I have no idea how to correct that issue.....maybe the IRS processing has some bug they'll fix later?

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Certainly, you can call TTX but they probably won't know how to fix it either:

What is the TurboTax phone number? (intuit.com)

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There are Tax Advocates nationwide you could contact, but make sure you have a full printout of your tax file first.

Taxpayer Advocate | Internal Revenue Service (irs.gov)