WAP_PUSH_DELIVER Intent never sent by Android system

I spent 5 hours attempting to make a custom MMS Broadcast receiver work. I googled and searched here at Stackoverflow a gazillion of seemingly duplicate threads but non of the workarounds or proposed solutions.

A few random debugging notes:

• The app is set as default SMS app and all permissions were granted.
• Verified that RCS is disabled through Google's Messenger.
• The DUT is a Pixel 3 XL with latest software updates.
• Tested many 3P SMS/MMS apps, almost all aren't able to receive MMS either, however, Pulse does. Pulse's developer provides an Open Source MMS library. I tried leveraging this library without success. The core problem seems to be that WAP_PUSH_DELIVER Intents are not sent to my application.
• Decoded the Pulse app to have a look at its AndroidManifest.xml and try a few different changes in mine. No success.
• Test MMS were sent with Google Voice account via legacy Hangouts and from other Android phones via various carriers.
• SMS can be received without problems both SMS_RECEIVED and SMS_DELIVER (if the app is the default SMS one).
• WAP_PUSH_RECEIVED events are received if the app is not the default SMS one
• WAP_PUSH_DELIVER events are not received if the app is the default SMS one
• Installed Intent Intercepter and ran $ adb logcat | fgrep -i intent to verify if any permission problems are logged. None are.

MmsReceiver:

public class MmsReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        System.out.println("MMS Received: " + intent.getAction());
    }
}

Manifest:

<uses-permission android:name="android.permission.SEND_SMS" />
<uses-permission android:name="android.permission.READ_SMS" />
<uses-permission android:name="android.permission.WRITE_SMS" />
<uses-permission android:name="android.permission.RECEIVE_SMS" />
<uses-permission android:name="android.permission.RECEIVE_MMS" />
<uses-permission android:name="android.permission.BROADCAST_WAP_PUSH" />
<uses-permission android:name="android.permission.BROADCAST_SMS" />
<uses-permission android:name="android.permission.RECEIVE_WAP_PUSH" />
<uses-permission android:name="android.permission.WRITE_APN_SETTINGS" />
<uses-permission android:name="android.permission.READ_PHONE_STATE" />
<uses-permission android:name="android.provider.Telephony.SMS_RECEIVED" />
<uses-permission android:name="android.permission.WAKE_LOCK" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
<uses-permission android:name="android.permission.CHANGE_WIFI_STATE" />
<uses-permission android:name="android.permission.CHANGE_NETWORK_STATE" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_SETTINGS"/>


    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.SEND" />
                <action android:name="android.intent.action.SENDTO" />

                <category android:name="android.intent.category.DEFAULT" />
                <category android:name="android.intent.category.BROWSABLE" />

                <data android:scheme="sms" />
                <data android:scheme="smsto" />
                <data android:scheme="mms" />
                <data android:scheme="mmsto" />
            </intent-filter>
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <receiver
            android:name=".SmsReceiver"
            android:permission="android.permission.BROADCAST_SMS">
            <intent-filter>
                <action android:name="android.provider.Telephony.SMS_DELIVER" />
            </intent-filter>
        </receiver>

        <receiver
            android:name=".MmsReceiver"
            android:permission="android.permission.BROADCAST_WAP_PUSH">
            <intent-filter>
                <action android:name="android.provider.Telephony.WAP_PUSH_DELIVER" />
                <data android:mimeType="application/vnd.wap.mms-message" />
            </intent-filter>
        </receiver>

        <service
            android:name=".HeadlessSmsSendService"
            android:exported="true"
            android:permission="android.permission.SEND_RESPOND_VIA_MESSAGE" >
            <intent-filter>
                <action android:name="android.intent.action.RESPOND_VIA_MESSAGE" />
                <category android:name="android.intent.category.DEFAULT" />

                <data android:scheme="sms" />
                <data android:scheme="smsto" />
                <data android:scheme="mms" />
                <data android:scheme="mmsto" />
            </intent-filter>
        </service>
    </application>

</manifest>

Needless to mention, the message is not logged in Logcat.

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