I am running companion app on Android 9, Phone is a DOOGEE S95Pro.
The app appears to stop running (the phone is not restarted) and as a result I am often not getting notifications until I access the app manually (by clicking on the app to start/restart it).
Battery optimization is switched off for the app. It happens both when I am on my WiFi or using mobile data.
Other symptoms include the app not updating sensors such as location or battery level until the app is selected.