It is really not possible to know the reason why that happened 2 years ago at this point.
Unless you had a distribution from the Traditional IRA in 2018 or 2019 and the 8606 form has the wrong line 2 amount then simply switch to the forms mode for the 2019 tax return and on the IRA Information Worksheet line 12 change it to the correct amount.
If you did have a 2018 distribution and the 8606 taxable amount is incorrect, then you would need to amend and make that change for 2018 so the correct tax is calculated on the 8606 form and then use the new 8606 line 14 amount to enter into 2019.
Are you trying to file a 2018 tax return using the 2018 CD/download software? Do you have the 2017. tax2017 data file on your computer and transferred form that?
Thanks for your reply! 2018 & 2019 returns filed/accepted. Just discovered the error. I have the .tax2017 data file. The cost basis data for spouse's traditional IRA transferred from 2017 file into 2018 & 2019, as well as the cost basis data for both of our Roth IRAs. The only thing missing is my traditional IRA cost basis, which doesn't show up in the worksheets for 2018/2019.
It is really not possible to know the reason why that happened 2 years ago at this point.
Unless you had a distribution from the Traditional IRA in 2018 or 2019 and the 8606 form has the wrong line 2 amount then simply switch to the forms mode for the 2019 tax return and on the IRA Information Worksheet line 12 change it to the correct amount.
If you did have a 2018 distribution and the 8606 taxable amount is incorrect, then you would need to amend and make that change for 2018 so the correct tax is calculated on the 8606 form and then use the new 8606 line 14 amount to enter into 2019.