Hi there! I am having a similar problem too. I use DeviceActivityMonitor to set 15 minute sessions for removing apps' shield. After 15-minute session is done, shield doesn't apply reliably in my internal testers. It applies if the tester is in my app or in blocked app but it doesn't if user's phone is locked or they are using another app. Although in my device it applies successfully when I build it from Xcode. This made me think whether this is a provisioning/build issue or a reliability issue (of device activity extension).