Unity 5 - Google Play NO Authentication

Hi UnityAnswers,

I've did quite a bit of research into this and can't find a solution that works for me. I've had Google Play Services working in my current game (logging in + leaderboards). However, with the recent addition of AdMob into my project, the app doesn't log the player in.

I did some quick debugging, and it appears that it's neither succeeding or failing. It just seems to hang.

Here is my simple code:

 void Start()
         {
             PlayGamesPlatform.Activate();
             Social.localUser.Authenticate(ProcessAuthentication);
         }
 
    void Login()
     {
         Social.localUser.Authenticate(ProcessAuthentication);
     }
 
     public void LoadLeaderboard()
     {
         if (Social.localUser.authenticated)
         {
             ((PlayGamesPlatform)Social.Active).ShowLeaderboardUI(boardID);
         }
         else
         {
             Login();
         }
     }

Here is my logcat from when I press the leaderboard button. I know this is after the initial auto-attempt at signing in, but because it doesn't authenticate, the button will attempt to sign in again:

 I/Unity   (31198): DllNotFoundException: gpg
 I/Unity   (31198):   at (wrapper managed-to-native) GooglePlayGames.Native.Cwrapper.Builder:GameServices_Builder_Construct ()
 I/Unity   (31198):   at GooglePlayGames.Native.PInvoke.GameServicesBuilder.Create () [0x00000] in <filename unknown>:0
 I/Unity   (31198):   at GooglePlayGames.Native.NativeClient.InitializeGameServices () [0x00000] in <filename unknown>:0
 I/Unity   (31198):   at GooglePlayGames.Native.NativeClient.Authenticate (System.Action`1 callback, Boolean silent) [0x00000] in <filename unknown>:0
 I/Unity   (31198):   at GooglePlayGames.PlayGamesPlatform.Authenticate (System.Action`1 callback, Boolean silent) [0x00000] in <filename unknown>:0
 I/Unity   (31198):   at GooglePlayGames.PlayGamesPlatform.Authenticate (System.Action`1 callback) [0x00000] in <filename unknown>:0
 I/Unity   (31198):   at GooglePlay.Login () [0x00000] in <filename unknown>:0
 I/Unity   (31198):   at GooglePlay.LoadLeaderboard () [0x00000] in <filename unknown>:0
 I/Unity   (31198):   at UnityEngine.Events.InvokableCall.Invoke (System.Object[] args) [0x00000] in <filename unknown>:0
 I/Unity   (31198):   at UnityEngine.Events.InvokableCallList.Invoke (System.Object[] parameters)

Thanks for any help! It's just so frustrating, having released two mobile games in the past and now running into these really weird problems ... >.>