MoPub Network Ads Attempts showing 300+ but impression is 0?



I have integrated the AdMob with MoPub as a external network to serve ads through MoPub, And now it is displaying ads on the iOS device and its also gets reflected on the counts example Attempts 300, Impression 270. But in android Attempts 300+ but the Impression 0 i don’t know why it is showing like this? Also ads are not getting displayed for android over version 5+(Lolipop), please refer the following configs that i have used to integrate with android.

MoPubSDK V - 4.1.0
Google Play Services - 7.0.0

Gradle Config :

 repositories {
 dependencies {
     //other integrations

     compile ''
     compile('com.mopub:mopub-sdk:4.1.0@aar') {
         transitive = true

And i have created MoPub AdUnit for every Activity on the App. the mobile like Xiaomi with Version 4.4 is displaying ads properly.

Please give me some solution, thanks.