Why cannot I receive push messages?

Check your agconnect-services.json

If you have made any changes at the Huawei Developer Console, such as setting the data storage location and enabling or managing APIs, you have to download the latest agconnect-services.json file and replace the existing file in the App directory.

Check the Signing Certificate Fingerprint

More imfo you could find at Huawei docs

Same app with HMS and FCM at the same device

If you are developing / testing HMS and FCM at the same device then better to remove cache for installed app, remove app and after that install build with other push cloud.