Apparent calculation error around Recover Rebate Credit

I followed your instructions to enter the stimulus payments that I received. Once I did, my refund went up substantially, presumably because that portion of my income wasn't taxable. However, the IRS says that TurboTax made a calculation error on the Recovery Rebate Credit and only gave me what showed prior to my entering the stimulus amounts. 

- We didn't make over the allowed amount

- Social Security numbers are correct

- Last names are fine

- No overage dependents

That just leaves "amount was computed incorrectly. 

I didn't do any computing and didn't enter anything in addition to what TT asked for. Can anyone explain why this happened?