After clicking the continue button on the Your 1099-R Entries, when asked you must also enter your December 31, 2019 balance in traditional IRA contributions.
Note that if you made any nondeductible traditional IRA contributions in 2019, TurboTax will probably use Worksheet 1-1 from IRS Pub 590-B to calculate the taxable amount, leave lines 6 through 12 of Form 8606 blank and will put an asterisk on lines 13 and 15 with the explanation for the asterisk below line 15.
If you are using the CD/download version of TurboTax or you have downloaded the pdf of your tax return with all worksheets, you can examine line 18 of the IRA Information Worksheet to see that it shows your year-end balance.
