Why does Polymorph stops an active Rage on a Barbarian (no more class features), but doesn’t remove Arcane Ward?Arcane Ward is an external effect that you activate. Its duration isn't dependent on your form.
— Jeremy Crawford (@JeremyECrawford) October 3, 2017
Nothing in the duration of Rage suggests it’s dependent on your form, either. What is it, specifically, about Arcane Ward that makes it “external” while Rage is not?
I think the point that he’s trying to make is that Rage affects your body, while Arcane Ward surrounds it and shields you. That would be the only explanation for why one works and the other doesn’t. I personally do not agree and believe that if Rage was begun before the shift, I’d let it continue. However, I wouldn’t let them end it early voluntarily, nor reactivate it once it’s done, since either of these actions is a Class Feature.