Update: I tried to replicate this on an Android 9 (Razer Phone 2). And this one DID save my changes. So as it turns out, this is a problem soley on the iOS app. Good to know.

But if it supports Bluetooth (which the U1 seems to be able to as well) then you could also connect it to a PC as long as it uses the HID profile, which it quite likely does. That is actually a feature you should look into utilizing since it is literally a useful side effect. Youtube Videos about the U1 have actually demonstrated this very usecase as well and it is super handy as a Kodi remote, for instance :) That is also the reason why I am going to be getting a U1.