Amount showing in the Northern residents/additional ded. line, however I can't find anything I have claimed in that section.

[thea-brown86]

I have not selected the Northern residents box.

[TurboTaxSusan]

Are you looking at the page “Here's your deductions summary”? If so the line “Northern residents/additional ded.” Is not just for the Northern Residents deduction (Line 25500), it includes Additional deductions (Line 25600) as well. If you have reported U.S. Social Security benefits, then that is what is showing on the page, not the Northern Residents deduction. This Canada Revenue Agency (CRA) webpage lists everything that is included in Additional deductions (Line 25600): Line 25600 – Additional deductions