java - Admob ads doesn't show on some android phones -

my interestitial ad , nativeexpressad doesn't show on few phones, have tested on few types of phones , worked on: nexus 6 android 6.0.1, xperia z3 compact android 4.4.3, emulator android 6.0, xperia j5 doesnt work on: xiaomi redmi note 2 android 5.0 , lg l5 custom rom android 6.0. code of interstitialad:

interestitialad = new interstitialad(getactivity());         interestitialad.setadunitid(getresources().getstring(r.string.interstitial_ad));         adrequest adreq = new adrequest.builder()                 .addtestdevice(adrequest.device_id_emulator)                 .build();         interestitialad.setadlistener(new adlistener() {             @override             public void onadloaded() {                 super.onadloaded();                 interestitialad.show();             }         });         interestitialad.loadad(adreq); 

i considering fault of height , width when interstitalad doesn't need specify adsize. ye, phones had internet connection.