Check that MiFit app has all nessesary permisions, (location, notifications)
1. Open MIFit
2. Click profile
3. Click on Mi Band 3.
4. Open Application notification
5. Now open Application Management and add Messenger /Whatsapp
6. Restart Phone and connect to Mi Band.
If this does not work, contact us
I have added, Viber, Yandex mail and MiFit.