Google Maps not shown for application downloaded from Play Store

Hello guys,
I’m using Ionic Google Maps, with this configuration:
Ionic CLI:4.10.3

"@ionic-native/core": "^4.15.0",
"@ionic-native/google-maps": "^4.15.1",
"@ionic-native/splash-screen": "4.15.0",
"@ionic-native/status-bar": "4.15.0",
"cordova-plugin-googlemaps": "2.5.2",

  "cordova-plugin-googlemaps": {

I have a strange issue (OK:Map displayed)
Application in Simulator :OK
Application installed using signed apk just before deploying to Google Play: OK.
Application installed using Google Play (the same apk as in step 2) : NOT OK. Map not displayed

Map page is accessed using tabs or using NavController.push.

For information: I was using ionic/native 4.18.0 but downgraded to 4.15.0
Before downgrading I hade this in config.xml:

<plugin name="cordova-plugin-googlemaps" spec="2.5.2">
    <variable name="API_KEY_FOR_ANDROID" value="XXXX" />
    <variable name="API_KEY_FOR_IOS" value="XXXX" />
    <variable name="PLAY_SERVICES_VERSION" value="15.0.1" />
    <variable name="ANDROID_SUPPORT_V4_VERSION" value="27.+" />

After deleing node_modules and installing (npm install), the variables PLAY_SERVICES_VERSION and ANDROID_SUPPORT_V4_VERSION dispaeared. (It was not working also when having ionic/naitve 4.18.0 and these two variables present in config.xml).

Thank you for your help.