Hi there,
I think I figured out where the problem is.
By going to the "IRA Information Worksheet", I found line 12 is $6000 and line 13 (adjustment due to return of excess amount) is $6000 too, which made line 17 adjusted total basis to 0.
In my case, since I made $12000 contribution to traditional IRA in 2019 and the withdrawal of excess amount happened in 2020, so as of Dec, 31, 2019, my IRA basis should be $12000, instead of $6000, because all the money was left in that account. If I put down my IRA basis to $12000 instead of $6000, then everything is back to normal.
