I had the same problem, too.
In my return, the entry on line 12900 of the T1 General form and I found it on the Home Buyers' Plan Worksheet.
When clicking on the cell entry for line 12900 (which I didn't enter myself) - I was taken to the T4RSP data entry sheet which was blank.
So, I was glad to see your email explaining where the the entry on line 12900 originated. It was not user friendly to find in TurboTax. Perhaps TurboTax could be modified to help users find where the data on line 12900 originated (if not on the T4RSP worksheet).
