Diagnosis
The scooter's Bluetooth module has glitched or the phone's cache is corrupted.
How to Fix It
Reset the scooter's Bluetooth. Turn the scooter on. Press and hold the power button and throttle lever together for 10 seconds until the Bluetooth icon on the display blinks. Then try pairing again.
If That Didn't Work
Delete the scooter from your phone's Bluetooth settings AND from within the Mi Home app. Force close the app. Restart your phone. Then try the pairing process from scratch.
Heads Up
Bluetooth connection is only for app settings. Riding functionality does not depend on it. Do not waste time fixing this before a ride.