Hey @tigerflame, 
Thank for your post. There are a few reasons why your device may not be syncing to Strava.

• Your device may not be connected to the phone via Bluetooth.
• Your device may have been disconnected from Strava.
• Bad data coverage areas can cause sync issues.

To check if your device is connected to the phone via Bluetooth, for Android, go to Settings > Connections > Bluetooth and look for your device. For iOS, go to Settings > Bluetooth and under My devices look for your device.
 
To check permissions, on your phone, go to Settings > Applications. Check the permissions section of each app (Strava and Mi Fitness) to ensure all permissions have been granted.
 
Check your data coverage area, both Strava and Mi Fitness need an active internet connection to load, refresh or sync data between them. If syncing fails, check you are in a good data coverage area.
 
Confirm you have authorized Strava to sync with Mi Fitness. To do this,
Go to Profile > Connected apps. 
 
Make sure you have toggled the on switch for Strava. You will be asked to authorize the connection between the two devices. Use your Strava login to authorize the connection.
 
If you are still having issues syncing we encourage you to reach out to Mi Fitness support directly.