If your device is running Android 13, make sure you’ve granted notification permissions for the Energy Monitor app. The app is optimised for the new Android 13 rules as of version 4.5.34 (December 2022), and will request the necessary permissions when you open the app for the first time. If the app detects that permissions have not been granted, check the monitor settings menu and you’ll see an alert in red at the top of the screen; tap on it to go to the external app settings screen where you’ll be able to grant notification permissions.
Check your device settings (second tab in settings screen), and make sure there are no warnings under any of your alert settings.
In some cases, the performance of apps can be limited by Android and Wear OS after they’ve been running for long periods of time. In app versions 4.2 and up, try tapping ‘Restart monitors’ at the bottom the device settings menu. If that doesn’t fix the issue, try restarting your device.