exception.class.missing._Unknown_: Strongly consider using FLAG_IMMUTABLE without PendingIntent in source

Question

I recently updated my app to target API 31 and have noticed a new crash being reported in the Google Play Console that makes no sense to me.

The crash caused by exception.class.missing._Unknown_: Strongly consider using FLAG_IMMUTABLE... for which there are a number of answers on SO and elsewhere, however from what I have read this crash should be related to use of PendingIntent only.

The crash reports make sense in that I have only seen the crash reported on Android 12 (API 31) as this is where the explicit IMMUTABLE or MUTABLE requirement was introduced, but I have searched the whole of my project and cannot find any use of PendingIntent.

The timing of the crashes appears to tie in with an FCM push notification I sent, which again ties in with the crash coming from PendingIntent, but if I cannot find that in my source then how can I explicitly set FLAG_IMMUTABLE?

My project dependencies are as below:

dependencies {
    implementation fileTree(include: ['*.jar'], dir: 'libs')
    implementation 'androidx.legacy:legacy-support-v4:1.0.0'
    implementation 'androidx.appcompat:appcompat:1.4.0-beta01'
    implementation 'com.google.android.material:material:1.4.0'
    implementation 'com.google.code.gson:gson:2.8.6'
    implementation 'androidx.constraintlayout:constraintlayout:2.1.1'

    // billing for in-app purchases
    implementation 'com.android.billingclient:billing:3.0.2' 

    // For in-app review flow
    implementation 'com.google.android.play:core:1.10.2'

    // Import the Firebase BoM
    implementation platform('com.google.firebase:firebase-bom:26.1.1')
    implementation 'com.google.firebase:firebase-messaging'

}

Answer 1

This is a known issue with Admob, as mentioned at https://developers.google.com/admob/android/quick-start

androidx.work:work-runtime:2.1.0 pulled from play-services-ads has a bug using PendingIntent without FLAG_IMMUTABLE or FLAG_MUTABLE and will fail in apps targeting S+.

The solution is also mentioned, in the app/build-gradle file:

dependencies {
      implementation 'com.google.android.gms:play-services-ads:20.4.0'
    
      // For apps targeting Android 12, add WorkManager dependency.
      constraints {
        implementation('androidx.work:work-runtime:2.7.0') {
            because '''androidx.work:work-runtime:2.1.0 pulled from play-services-ads
                       has a bug using PendingIntent without FLAG_IMMUTABLE or
                       FLAG_MUTABLE and will fail in apps targeting S+.'''
        }
      }
    }