Continuity mistake: Before Kara uses her heat vision against Vartox she gets some dust on her suit, then she stands up and the dust is gone.
Continuity mistake: When Cat is on the talk show, the microphone on her collar keeps disappearing and reappearing between shots.
Continuity mistake: When Alex brings donuts to try to convince Kara to come back to the D.E.O., Kara picks up 2 donuts which suddenly change to 1 once she sits down, and then back to 2 a few shots later in a wide shot.
The Adventures of Supergirl - S2-E1
Continuity mistake: When Kara saves the chopper the sun on the floor changes between shots.
Continuity mistake: When Vartox starts to fight Kara the sun changes between shots.
Continuity mistake: When Vartox attacks Kara from behind the background changes in the next shot.
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.