Files in /res/raw not found. Removed in release bundle

The bundle in release does not generate the res/raw folder. Therefore, libraries like PushNotification that read the sound from that folder do not work correctly.

I need the audio.mp3 file to exist in the release bundle inside the res/raw folder

The problem only exists in the release bundle. In the debug bundle it works correctly.

I show how the folder structure is inside the apk in a bundle made with debug. Notice how the audio.mp3 file exists.

.
└── apk
    ├── assets
    │   └── ...
    ...
    ...
    │   └──  ...
    └── res
        ├── color
        ├── color-night-v8
        ├── color-v21
        ├── color-v23
        └── color-v31
        └── raw
            ├──  audio.mp3

Now I show how is the folder structure inside the apk in a bundle made with release. See how the raw folder does not exist

.
└── apk
    ├── assets
    │   └── ...
    ...
    ...
    │   └──  ...
    └── res
        ├── color
        ├── color-night-v8
        ├── color-v21
        ├── color-v23
        └── color-v31

This means that the push notification will not sound with the custom audio.

Replication

Here I present a repository with a simple project of an ionic app that reproduces the mentioned error.

https://github.com/WilmerRS/ionic-push-notification-raw-files

Build, create apk as release and review the generated apk.

Aditional Context

This is the configuration tried so that the audio.mp3 file is not removed from the bundle in release. It has not achieved any effect.

Keep file, android/app/src/main/res/raw/keep.xml

<?xml version="1.0" encoding="utf-8"?>
<resources tools:keep="@raw/audio.mp3, @raw/audio, @raw/*"
  xmlns:tools="http://schemas.android.com/tools">
</resources>

Proguard rules android/app/proguard-rules.pro

-keepclassmembers class **.R$* {public static <fields>;} 
-keep class **.R$*