I sit in a quiet library room and want to see online videos with my smartphone. I turn the volume down with side volume button. But after I open a video App, like YouTube, Bilibili, TikTok, my phone will remember the volume level the last time i used on this App. The sound volume exploded out and everybody looked at me. I'm using Huawei Nova 3 and Android OS 9. I don't know why the App on this phone don't use the system volume level I set for now, or retrieve the last time volume setup. Hope people here can help me.