Doesn't work on Galaxy S5 but works on other android devices

After a week of doing this and that, I believe it's a compatibility issue with S5 and Unity Ads (Unity 5). To test, you can either use Unity's Nikolai's sample (https://github.com/wcoastsands/unity-ads-demo), or I created the simplest project with a button to show ads which you can download from the link below.

Device Log: Please see link below.

Result S5: Ad seems to be ready as it passes isReady validation but it just reloads the scene.
Galaxy Nexus/Xperia 2: No problem on both.

Note that I tried both test and live ad. Both debug and release builds. No difference.

Lastly note that, if you open any url on S5 from your Unity 5 app (say a link to rate app) and then press hardware back button, same result, Unity 5 reloads the entire scene. Not sure if it is related but seems like a view container issue.

Code (CSharp):

1.     void Awake(){
2.        
3.         if (Advertisement.isSupported && !Advertisement.isInitialized) {
4.            
5.             Advertisement.allowPrecache = true;
6.  
7.             // Setting test to false, dev build on etc don't have any effect
8.  
9.             #if UNITY_IPHONE
10.             Advertisement.Initialize(UNITY_AD_IOS, true);
11.             #elif UNITY_ANDROID
12.             Advertisement.Initialize (UNITY_AD_ANDROID, true);          
13.             #endif
14.            
15.         } else {
16.             Debug.Log ("Platform not supported");
17.         }
18.  
19.     }
20.  
21.     void Start () {
22.         adButton.onClick.AddListener(ShowUnityAd);
23.     }
24.    
25.  
26.     void ShowUnityAd(){
27.  
28.         if( Advertisement.isReady() ){
29.             Advertisement.Show(null, new ShowOptions(){ pause = true });
30.         }
31.  
32.     }

Test Project:
http://www.imagnity.com/wp-content/uploads/2015/04/UnityAdsTestS51.zip
Device Log:
http://www.imagnity.com/wp-content/uploads/2015/04/UnityAdsTest_DeviceLogs.txt