The Bluetooth connection between the band and the phone encounters disruptions or inconsistencies, making the band temporarily undetectable.
For your reference, here are two resolutions for this issue as follows:
1. Manually toggling the Bluetooth switch on the phone's system settings can help reset the Bluetooth connection and clear any existing connection errors or conflicts;
2. Restarting both the Xiaomi Smart Band 9 and the phone can also resolve connectivity issues by refreshing their operating states and allowing them to reconnect properly.