If a Huawei device is supporting both GMS and HMS core then why HMS core is not working?

I am developing an app for android, on Huawei devices I am facing many issues. I am using FusedLocation and Notifications in my app due to which I had to develop another app for Huawei devices as many Huawei devices are not supporting GMS now. I am unable to understand the main difference between HMS and GMS.

• If a Huawei device is containing both GMS and HMS and app is downloaded from App Gallery (that contains HMS support) then HMS core will cause some issues. Notifications and Location callback will not work correctly.
• If a device contains only HMS core and app is downloaded from AppGallery then it will work fine.

You are advised to use the solution for integrating both GMS and HMS. The advantages are as follows:

1. Reduce the complexity of app packaging. A package can be released to both Google Play and HUAWEI AppGallery.
2. Reduce the code maintenance cost. The HMS+GMS adaptation layer code is added to the original logic code. In this way, proper code can be automatically called based on the mobile phone. That is, you do not need to modify existing logic code or maintain two sets of code.

It is recommended that you use HUAWEI HMS ToolKit, which can help you quickly add the HMS+GMS adaptation layer code and upgrade your logic code to support both GMS and HMS.

For details, You may refer to this question: Have both GMS and HMS in the project.