Why does Huawei mate40 always automatically lower the ringtone after upgrading the HarmonyOS system?

Why does Huawei mate40 always automatically reduce ringtones after upgrading to HarmonyOS system? In the meantime, the ringtone volume will automatically drop to about 30%, and I have been looking for the reason. I was puzzled for several days, and finally determined the reason through continuous testing. It is because watching the screen reduces the volume of incoming calls, and picking up the phone reduces the volume. When the screen is on, the volume of the bell will automatically decrease and then it will turn on. This will not happen if you just hang up the screen and turn on the volume of incoming calls. At present, until this bug is fixed, I don't want the ringtone volume to drop automatically.