1. It's a general UMI OS issue related to the notification system and notification bar, regardless of the specific model and/or software version. It's being investigated by the developers.
2. It's related to the S2 Pro only but in all build versions. The developers are going to check how to optimize the too strict RAM management.
3. Better not to use that app or use the Lite version. Check its feedback posts.
Same for me - the vibration is so light I can't feel phone ringing in my pocket.
Also, I wasn't able to find any configuration for the vibration level, just the 'Also vibrate on calls'.