Some of my eligible mortgage interest is being disallowed by TurboTax. How do I troubleshoot and fix that in TurboTax when mortgage was refinanced in 2020-TurboTax error?

Possibly.

If you had no balance left because you paid it off, you would need to enter zero for the ending balance for that loan.

You can enter your 1098 Forms into the program in the federal section of the program.

1. Select Deductions & Credits
2. Select Mortgage Interest and Refinancing (Form 1098) 
3. At the bottom of the next page, select Add another 1098
4. Be sure to answer the questions carefully for each 1098

Be sure that you have entered $0 for the loan that was paid off in Box 2 - Outstanding mortgage principal on the screen titled Let's get the details from your Home loan 1098.

You will also want to select that the loan is no longer there at the end of the year is marked as paid off during the year.

Please see the link below for more information on the mortgage interest deduction.

Deducting Home Mortgage Interest