Android : AdMob on Android fails to load the interstitial ad and print several warnings

I am trying to put an interstitial ad in my android app. I followed the tutorial provided by the official site and everything was working properly.

https://developers.google.com/mobile-ads-sdk/docs/admob/android/interstitial

Then, suddendly with no changes on the code (which is exactly the one in the tutorial), it started to fail in loading the ad and giving a lot of warnings:

04-17 11:10:29.101: I/dalvikvm(7698): Could not find method android.app.AppOpsManager.checkPackage, referenced from method com.google.android.gms.common.GooglePlayServicesUtil.zza
04-17 11:10:29.101: W/dalvikvm(7698): VFY: unable to resolve virtual method 110: Landroid/app/AppOpsManager;.checkPackage (ILjava/lang/String;)V
04-17 11:10:29.101: D/dalvikvm(7698): VFY: replacing opcode 0x6e at 0x0010
04-17 11:10:29.101: I/dalvikvm(7698): Could not find method android.content.pm.PackageManager.getPackageInstaller, referenced from method com.google.android.gms.common.GooglePlayServicesUtil.zzg
04-17 11:10:29.101: W/dalvikvm(7698): VFY: unable to resolve virtual method 471: Landroid/content/pm/PackageManager;.getPackageInstaller ()Landroid/content/pm/PackageInstaller;
04-17 11:10:29.101: D/dalvikvm(7698): VFY: replacing opcode 0x6e at 0x000b
04-17 11:10:29.321: I/dalvikvm(7698): Could not find method android.app.AppOpsManager.checkPackage, referenced from method com.google.android.gms.common.ff.a
04-17 11:10:29.321: W/dalvikvm(7698): VFY: unable to resolve virtual method 127: Landroid/app/AppOpsManager;.checkPackage (ILjava/lang/String;)V
04-17 11:10:29.321: D/dalvikvm(7698): VFY: replacing opcode 0x6e at 0x0012
04-17 11:10:29.321: I/dalvikvm(7698): Could not find method android.content.pm.PackageManager.getPackageInstaller, referenced from method com.google.android.gms.common.ff.a
04-17 11:10:29.321: W/dalvikvm(7698): VFY: unable to resolve virtual method 479: Landroid/content/pm/PackageManager;.getPackageInstaller ()Landroid/content/pm/PackageInstaller;
04-17 11:10:29.321: D/dalvikvm(7698): VFY: replacing opcode 0x6e at 0x000d
04-17 11:10:29.321: D/dalvikvm(7698): DexOpt: --- BEGIN 'ads-1881740967.jar' (bootstrap=0) ---
04-17 11:10:29.401: I/Ads(7698): Starting ad request.
04-17 11:10:29.711: D/dalvikvm(7698): DexOpt: --- END 'ads-1881740967.jar' (success) ---
04-17 11:10:29.711: D/dalvikvm(7698): DEX prep '/data/data/com.myapp.zsp/cache/ads-1881740967.jar': unzip in 0ms, rewrite 390ms
04-17 11:10:29.801: I/Ads(7698): CsiReporterFactory: CSI is not enabled. No CSI reporter created.
04-17 11:10:35.151: I/dalvikvm(7698): Could not compile trace for Ljava/util/Arrays;fill, offset 5
04-17 11:10:35.151: D/dalvikvm(7698): ++++++++++++++++++++++++++++++++++++++++++++
04-17 11:10:35.151: D/dalvikvm(7698): JIT_INFO: Issues while compiling trace  Ljava/util/Arrays;fill, offset 5
04-17 11:10:35.151: D/dalvikvm(7698):   The trace provoked a spill.
04-17 11:10:35.151: I/dalvikvm(7698): Trying less registerization from 1 to 0
04-17 11:10:35.151: D/dalvikvm(7698): JIT_INFO: Retrying trace Ljava/util/Arrays;fill, offset 5
04-17 11:10:35.151: D/dalvikvm(7698): ++++++++++++++++++++++++++++++++++++++++++++
04-17 11:10:40.431: W/Ads(7698): There was a problem getting an ad response. ErrorCode: 0
04-17 11:10:40.431: I/dalvikvm(7698): Could not find method android.webkit.WebSettings.setMixedContentMode, referenced from method com.google.android.gms.ads.internal.s.g.<init>
04-17 11:10:40.431: W/dalvikvm(7698): VFY: unable to resolve virtual method 3153: Landroid/webkit/WebSettings;.setMixedContentMode (I)V
04-17 11:10:40.431: D/dalvikvm(7698): VFY: replacing opcode 0x6e at 0x004a
04-17 11:10:40.441: I/dalvikvm(7698): Could not find method android.webkit.WebView.evaluateJavascript, referenced from method com.google.android.gms.ads.internal.s.g.evaluateJavascript
04-17 11:10:40.441: W/dalvikvm(7698): VFY: unable to resolve virtual method 3164: Landroid/webkit/WebView;.evaluateJavascript (Ljava/lang/String;Landroid/webkit/ValueCallback;)V
04-17 11:10:40.441: D/dalvikvm(7698): VFY: replacing opcode 0x6f at 0x0016
04-17 11:10:40.441: I/dalvikvm(7698): Could not find method com.google.android.gms.ads.internal.s.g.isAttachedToWindow, referenced from method com.google.android.gms.ads.internal.s.g.onDraw
04-17 11:10:40.441: W/dalvikvm(7698): VFY: unable to resolve virtual method 5758: Lcom/google/android/gms/ads/internal/s/g;.isAttachedToWindow ()Z
04-17 11:10:40.441: D/dalvikvm(7698): VFY: replacing opcode 0x6e at 0x000c
04-17 11:10:40.551: W/Ads(7698): Failed to load ad: 0

The current version of Google Play Services that I am using is 7.0 with specific version number 7095000.

I am currently testing on a real device: Asus Zenfone 6 with Android 4.3.

Any idea is appreciated.