Deadlock when using runBlocking coroutine for retrieve Firebase's AuthUI.signOut() result

Question

I currently learning how to use Kotlin coroutines for Android applications. And one of the things that fascinates me a lot is a possibility to treat asynchronous procedures synchronously.

So, my toy application based on MVVM architecture pattern and using Firebase to implement sign in/out functionality. And there is a SignOut use case:

class FirebaseSignOut @Inject constructor(private val firebaseAuthUi: AuthUI) : SignOut {
    private lateinit var signOutResult: SignOutResult

    override fun execute(context: Context): SignOutResult {
        runBlocking {
            signOutResult = getSignOutResult(context)
        }

        return signOutResult
    }

    private suspend fun getSignOutResult(context: Context): SignOutResult {
        return suspendCoroutine { continuation ->
            firebaseAuthUi.signOut(context)
                    .addOnSuccessListener {
                        continuation.resume(SignOutSuccess)
                    }
                    .addOnFailureListener {
                        continuation.resume(SignOutError)
                    }
                    .addOnCanceledListener {
                        continuation.resume(SignOutCancel)
                    }
        }
    }

}

The problem

is that blocking started with runBlocking is never unlocks.

I have figured out that coroutines logic itself is not a problem by replacing getSignOutResult() by mock, for example:

private suspend fun getSignOutResult(context: Context): SignOutResult {
    delay(500)
    return SignOutError
}

Then I was able to track the blocking til this part of Firebase's AuthUI:

return Tasks.whenAll(
        signOutIdps(context),
        maybeDisableAutoSignIn
).continueWith(new Continuation<Void, Void>() {

https://github.com/firebase/FirebaseUI-Android/blob/master/auth/src/main/java/com/firebase/ui/auth/AuthUI.java#L325

private Task<Void> signOutIdps(@NonNull Context context) {
    ...
    return GoogleSignIn.getClient(context, GoogleSignInOptions.DEFAULT_SIGN_IN).signOut();
}

https://github.com/firebase/FirebaseUI-Android/blob/master/auth/src/main/java/com/firebase/ui/auth/AuthUI.java#L403

and figure out that maybeDisableAutoSignIn Task is never starts. So, deadlock happening somewhere inside GoogleSignIn's signOut(), which is unable to trace.

Question

Does anybody have an idea why such a deadlock can possibly happen? And any suggestion how to solve the problem is greatly welcome.

Configuration details

I use currently latest versions of Kotlin and Firebase libraries

firebaseCoreVersion = '16.0.4'
firebaseUiVersion = '4.1.0'
kotlinVersion = '1.3.0'
kotlinCoroutinesVersion = '1.0.0'

AuthUI settled to use only Google sign in.

---

! PLEASE NOTE that I know I can make signOutResult variable observable. But in this case execute will not be able to return a result. And I really want to do it because such implementation is easy mockable for tests. And the fact that runBlocking blocks main thread for a sign out is acceptable in my case - it makes sense that UI is unavailable during the procedure, since user interface changes significantly depending on authentication state.