Same here. Filed as FB8915855.

Still running into this today. It looks like this is fixed as of iOS 11.3, so to support older versions, I have this method in my UIPresentationController subclass: internal func animateDimmingViewDisappearing() {     guard let dimmingView = dimmingView,         let transitionCoordinator = presentedViewController             .transitionCoordinator         else { return }     // Despite this API being available earlier, iOS 11.3 is the first OS     // that doesn’t just animate this instantly.     if #available(iOS 11.3, *) {         transitionCoordinator.animateAlongsideTransition(             in: dimmingView.superview,             animation: { _ in dimmingView.alpha = 0 },             completion: { _ in dimmingView.removeFromSuperview() }         )     } else {         UIView.beginAnimations("animateDimmingViewDisappearing",                                context: nil)         if transitionCoordinator.transitionDuration > 0 {             UIView.setAnimationDuration(                 transitionCoordinator.transitionDuration             )         }         else {             UIView.setAnimationDuration(1.0 / 3.0)         }         UIView.setAnimationCurve(transitionCoordinator.completionCurve)         dimmingView.alpha = 0         UIView.commitAnimations()     } }