Looks like there is an annoying bug (does not affect numbers on my return) on the Deductions & Credits summary page (after you finish entering your Federal deductions).
In my case, it lists all my deductions (QBI, Standard Deduction, Self-Employed Health Insurance, & State and Local taxes greater than $10,000) and provides a total. Under the "State and Local taxes greater than $10,000" it shows a negative value that is less than $10,000 (-$N,NNN) and the column implies that it would be subtracted from the other deductions (which it shouldn't since its negative). In reality, the sum of the deductions shown does not include this negative value which is where the bug comes in.
The State and Local taxes should be listed on this summary page as $0 if the value is negative.