Fixed - Clicked on "Other Income Sources" which lists a bunch of options, including:
Foreign Income Verification Statement (T1135)
This box beside it was NOT ticked, though I had at this point said I do NOT own any foreign property to the earlier question, it was still making me fill out a T1135 as an "error" at the very end.
Now I ticked that it DID apply to me, went back, un-ticked that it applied, and then went to the very end and the errors were gone.
