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.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
