Google Play Games plugin doesn't initialize

[Starbox]

Have you found a solution? I have a logcat running alongside a plugged in Android device, I got the same issue.

3076 Error Unity AndroidJavaException: java.lang.ClassNotFoundException: com.google.android.gms.games.PlayGames
3076 Error Unity java.lang.ClassNotFoundException: com.google.android.gms.games.PlayGames
3076 Error Unity at java.lang.Class.classForName(Native Method)
3076 Error Unity at java.lang.Class.forName(Class.java:400)
3076 Error Unity at com.unity3d.player.UnityPlayer.nativeRender(Native Method)
3076 Error Unity at com.unity3d.player.UnityPlayer.access$300(Unknown Source)
3076 Error Unity at com.unity3d.player.UnityPlayer$e$1.handleMessage(Unknown Source)
3076 Error Unity at android.os.Handler.dispatchMessage(Handler.java:98)
3076 Error Unity at android.os.Looper.loop(Looper.java:154)
3076 Error Unity at com.unity3d.player.UnityPlayer$e.run(Unknown Source)
3076 Error Unity Caused by: java.lang.ClassNotFoundException: Didn’t find class “com.google.android.gms.games.PlayGames” on path: DexPathList[[zip file “/data/app/<app_bundle>-1/base.apk”],nativeLibraryDirectories=[/data/app/com.<app_bundle>-1/lib/arm64, /data/app/<app_bundle>-1/base.apk!/lib/arm64-v8a, /system/lib64, /vendor/lib64]]
3076 Error Unity at dalvik.system.BaseDexClassLoader.findClass

Having a few custom files for Gradle and one for Proguard, the latter already modified with this amount of text , has changed nothing. Force resolve didn’t change anything either.
The game uses a valid Unity project ID and is linked (otherwise using a debug key made it utterly impossible to run ‘Force Resolve’).