Hello!
First of all, thank you very much for your feedback!
We are currently working on an update to fix this issue, which should be available very soon.
I’ll keep you updated about the state of the update here too.
Regarding the notification:
As Christian stated correctly, we need the foreground notification to keep the app alive.
One thing you can do however is to remove the notification icon from the statusbar.
On most devices this can be done by opening the notification center (pull down from top) and long pressing the nuki notification, then choose “Minimize”.
Thank you for your patience!