ClassNotFoundException: “androidx.work.impl.WorkManagerInitializer”

A new exception appeared on some devices after upgrading Google AdMob Ads library version 19.4.0 to 19.5.0:

Caused by java.lang.ClassNotFoundException 
Didn't find class "androidx.work.impl.WorkManagerInitializer" on path: ...
dalvik.system.BaseDexClassLoader.findClass (BaseDexClassLoader.java:196)
androidx.core.app.CoreComponentFactory.instantiateProvider (CoreComponentFactory.java)
android.app.ActivityThread.installProvider (ActivityThread.java:7213)
android.app.ActivityThread.installContentProviders (ActivityThread.java:6769)
com.android.internal.os.ZygoteInit.main (ZygoteInit.java:941)

The exception appeared on devices with Android 8 & 10.

AdMob library 19.5.0 adds dependency on WorkManager 2.1.0 (via Play Services Ads Lite library): https://mvnrepository.com/artifact/com.google.android.gms/play-services-ads-lite/19.5.0

There is a similar question on this issue, but it seems to be unrelated (older Android OS versions with multiple dex, while here it's single dex and newer OS versions).

For now I downgraded to AdMob 19.4.0, which does not include WorkManager dependency.

Update (2020.12.18)

• The exception frequency is 1 per 1000 devices running Android 10.
• Forcing WorkManager 2.4.0 (instead of 2.1.0) also generates the exception.
• The issue is unrelated to AdMob. Adding WorkManager to the project with AdMob 19.4.0 reproduced the issue.
• My current assumption is that the issue is caused by a collision between the content providers of AudienceNetwork & WorkManager. Adding AudienceNetwork to a project with WorkManager generated a same exception, with a different class: Didn't find class "com.facebook.ads.AudienceNetworkContentProvider" on some Android 10 devices.

Workaround: manual initialization of WorkManager does not cause this exception.

AdMob 20.5.0 and above (or explicit dependency of WorkManager 2.6.0+)

WorkManager now uses App Startup provider. In order to use manual init:

1. Remove WorkManager from the App Startup provider.
2. Add WorkManager configuration to the Application object.

Step 1: There are 2 ways to remove WorkManager from the App Startup provider:

• Removing the entire provider. or
• Remove only WorkManager.

From the documentation of WorkManager:

 <!-- If you want to disable android.startup completely. -->
 <provider
    android:name="androidx.startup.InitializationProvider"
    android:authorities="${applicationId}.androidx-startup"
    tools:node="remove">
 </provider>

Or

 <provider
    android:name="androidx.startup.InitializationProvider"
    android:authorities="${applicationId}.androidx-startup"
    android:exported="false"
    tools:node="merge">
    <!-- If you are using androidx.startup to initialize other components -->
    <meta-data
        android:name="androidx.work.WorkManagerInitializer"
        android:value="androidx.startup"
        tools:node="remove" />
 </provider>

Step 2: Add manual WorkManager configuration in the Application object:

class MyApplication extends Application implements Configuration.Provider {
    @NonNull
    @Override
    public Configuration getWorkManagerConfiguration() {
        return new Configuration.Builder()
                .build();
    }
}

AdMob 20.4.0 and below

Remove the WorkManager default content provider initialization by adding the following to the Manifest.xml:

<provider
    android:name="androidx.work.impl.WorkManagerInitializer"
    android:authorities="${applicationId}.workmanager-init"
    tools:node="remove"
    android:exported="false"
    />

Add manual initialization of the WorkManager to the Application.onCreate() method:

Configuration myConfig = new Configuration.Builder()
        .build();
WorkManager.initialize(this, myConfig);