Why the Xiaomi Smart Band 9 doesn't alert some third-party APP messages?

For your reference, please check the following methods:
1. Check if the notification permission is enabled;
2. Check whether the phone has enabled the APP lock function. You need to turn off the setting of hiding notification content in the phone system.
Take the MIUI version for example: go to [Settings] >> [Apps] >> [App lock];
Take the Mi Fitness APP for example: check whether Mi Fitness APP has enabled the function of background lock/autostart. Phone messages cannot be synchronized to the band after disconnecting from the APP.