The Android designers don't like third party apps to unlock the phone. They are putting more and more restrictions over time, especially now with the 8 and 9 updates. Last time we got an email from Google Play complaining that we used the Lock/turn off the Screen feature in Android.
Anyway, the only way we could solve this would be to be a HID device (like a keyboard), so we simulate Enter Enter which would unlock the phone unless you have a PIN or similar. But we evaluated that and came to the conclusion that HID works very poorly in Android if we at the same time would like Flic to be an ordinary BLE device usable by the Flic app. (It's like the OS takes over the device connection etc., and it interferes with other apps; for example they might hide the on-screen keyboard). However, HID works good enough on iOS so there we use it for a couple of actions.