The battle for gaming creators has cost Amazon's Twitch another notable streamer: Corinna Kopf, a popular Instagram model, digital influencer and "Fortnite" Twitch streamer with millions of followers, is moving to Facebook Gaming under an exclusive agreement. On Facebook, Kopf's first stream is scheduled to take place Dec. 30 at 4 p.m. PT at facebook.com/gaming/corinnakopff. […]