Continuity mistake: The sketch that Brainy shows to Winn is meant to be his original sketch that he drew in the previous episode, hence why Winn is so shocked he's somehow got it. But it's slightly different from what we actually saw him draw at the time.
Continuity mistake: The shield design that Winn sketches on the paper changes between him starting to draw, and him showing it to his friend a second later.
Shelter from the Storm - S3-E18
Continuity mistake: When Winn and Brainy hug, Winn starts the hug with one arm high and one lower, towards Brainy's waist. The shot cuts and both his arms are up and in the centre of his body.
Answer: Another part of why the change was that it's cold in Canada in the winter and the old costume didn't protect her from it, whereas the new one is nice and warm.