Hi Theo and Pascar,
Theo: It does not sound like you are doing anything wrong. What is the signal strength displayed by the app? The connection to iOS is usually very stable when RSSI > -70dB or so. I am porting the new changes I made in Android over to the iOS app, there are some changes to connection handling that may fix the behavior, but it will be at least a week before I can release those updates. If it would be faster for you to exchange, please start that process with Elektor.
Pascar: Android bluetooth definitely has some “rough edges”, and unfortunately different manufacturer’s phones behave differently and we can’t test them all. I recommend joining the Android beta and trying again with the new app and firmware: https://play.google.com/apps/testing/com.mooshim.mooshimeter
You will have to do a firmware update, you can see a video of how to do that here:
Sorry for the inconvenience, please let me know how else I can help.