If u have observed that autofocus doesn't work in flyme camera app. So instead of that u can use Google camera for ur device which works well and video autofocus is working superb without any issues. Checkout the camera app, it is better than default camera.
In my m3 note video autofocus was not working so I tried this app and it works fine. If u have same issue like this in other meizu smartphone then u can solve by this Google camera application.

Download link: http://www.apkmirror.com/apk/google-inc/camera/camera-3-2-042-release/

Thank you