I've now determined the cause of the error. In an effort to determine estimated tax, I had created an initial estimated tax return which included the taxable SS income figure. When I modified this initial tax return to create the final return, the initial taxable SS figure was used (overridden) and I did not realize it nor do I recall the software app asking me to confirm that I wanted to use the overridden figure.
I should have reviewed the calculation worksheets as the overridden number is highlighted in red.
