The Mi Mix 2 is made by Xiaomi, and, at times, we've seen some odd behavior of our app on devices made by them.
One item that crops up on Android devices, regardless of manufacturer, is the Power Save mode, aka Battery Saver. Open up the Settings app and click on 'Battery & performance'. In there you should be to see if the phone is set up to save power by disabling the Covenant Eyes® app.
If you need help with that, please call/chat Customer Support at your convenience. Besides looking at the battery settings, a member of the team will have additional troubleshooting ideas to work through. If necessary, he/she will collect debug logs for further investigation.
The team is available Monday - Friday, 8 am to 11:45 pm (ET) and Saturday 10 am - 5:45 pm (ET). In the US you can call 877-479-1119. If you're outside the US, 989-720-8000.