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have you ever checked your firebase app indexing setting ?
on Android settings > Google account > scroll to bottom "firebase app indexing"
personally I open that and switch it OFF with all devices
have a wee gander also tap any Google app and then tap which ever items show
after switching off you can still go back every now and then and see what's going on
Firebase App Indexing gets your app into Google Search
more here about it
https://www.droidviews.com/firebase-app-indexing-setup-android/
and
https://www.techotopia.com/index.php/A_Firebase_App_Indexing_Tutorial