Consider the following snippet:

  Stack(
    alignment: AlignmentDirectional.center,
    children: <Widget>[
      UiKitView(/*...*/),
      Container(
        color: Colors.orange,
        width: 200,
        height: 200,
      ),
    ],
  );

Pointers that hit the container are not passed to RenderUiKitView, but on the platform side the FlutterTouchInterceptingView wrapping the UIView will block the touch sequence until the framework says to release it.
Since RenderUiKitView doesn't see the touch sequence it never sends the command to release the gesture.

cc @cyanglaz