App crashes in Android!

[ChristophSchmid05]

Hi guys
I'm facing the following problem.
I installed the plugin and as soon as I lock the screen on Android devices, the App crashes and I get the following:

E/AndroidRuntime: FATAL EXCEPTION: main Process: com.catapult.fitup, PID: 10870 java.lang.NoSuchMethodError: No static method metafactory(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite; in class Ljava/lang/invoke/LambdaMetafactory; or its super classes (declaration of 'java.lang.invoke.LambdaMetafactory' appears in /apex/com.android.runtime/javalib/core-oj.jar) at de.appplant.cordova.plugin.background.BackgroundModeExt.clearKeyguardFlags(BackgroundModeExt.java:387)

I also added
compileOptions { sourceCompatibility JavaVersion.VERSION_1_8 targetCompatibility JavaVersion.VERSION_1_8 }
to the build.gradle files!

Any ideas?