To keep the Xiaomi Watch S4 connected to the Mi Fitness APP, please refer to the following details:
1. Please keep the Mi Fitness APP in the APP whitelist in the APP settings on your phone;
2. Please keep the Mi Fitness APP running in the background without disabling the Bluetooth;
2. Please keep the watch and the phone connected in the available distance;
3. The setting methods are different for different phones. Please go to the [Mi Fitness] APP >> [Device] >> allow this APP to run in the background and follow the respective instruction to finish the settings.