This happened to me in 2020 as well, and I just stumbled across this glitch this week (late 2021) I have a jumbo mortgage (>$750K), and refinanced during 2020. TurboTax added the mortgages together, roughly doubling the actual average balance, and as a result my mortgage interest got shaved by many thousands, and my tax bill went up by several thousand $. I've just re-filed an amended 2020 return, and there I overrode the program to show the actual monthly average for each of the sequential mortgages.
I'm very disappointed and angry with TutboTax. This should've been part of their interview and error-checking, and easy to program. Had I not stumbled across this, I'd still be out several thousand bucks. As a 20-year Turbotax user, I'm truly pissed.
