Real ads not showing in release mode although the proguard is deactive. What may be the problem?

I registered to admob about 24 hours ago. Confirmation mail come from admob. I added admob id's to my app. When i install my app to a real device by clicking run button in android studio, the real ads showing properly. So my admob ids work correctly.

However, when i generate signed apk and install the apk to my device by apk install ... command using Android Studio terminal, real ads does not showing. I firstly think that the problem is related to proguard however it is not related to proguard. Because i deactivated proguard and the real ads still not showing. What may be the problem?

build.gradle (app level):

apply plugin: 'com.android.application'
apply plugin: 'com.bugsnag.android.gradle'

android {
    compileSdkVersion 28
    buildToolsVersion '28.0.3'
    defaultConfig {
        applicationId "...."
        minSdkVersion 16
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
        multiDexEnabled true
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
        debug {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(include: ['*.jar'], dir: 'libs')
    implementation 'com.android.support:appcompat-v7:28.0.0'
    implementation 'com.android.support:design:28.0.0'
    implementation 'com.android.support:recyclerview-v7:28.0.0'
    implementation 'jp.wasabeef:recyclerview-animators:2.2.4'
    implementation 'com.android.support:cardview-v7:28.0.0'
    implementation 'com.nex3z:flow-layout:1.1.0'
    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
    implementation 'com.google.android.gms:play-services-ads:17.1.1'
    implementation 'com.bugsnag:bugsnag-android:4.+'
}

build.gradle(project level)

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {
    repositories {
        google()
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.2.1'
        classpath 'com.bugsnag:bugsnag-android-gradle-plugin:3.+'
        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        google()
        jcenter()
        maven { url "https://maven.google.com" }
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

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