Are you entering mileage on a Schedule C for business expenses? As you enter your expenses, it is affecting your income and might be affecting other credits like earned income credit or additional child tax credit.
If you are entering mileage for your Schedule C business expense, then by entering the expense, you are reducing the Schedule C income. This, in turn, could be reducing your Qualified Business Income (QBI) deduction. Lowering the QBI deduction would increase your balance due.
I don't claim either of those, I am entering this under business and income expenses.