Battery saver restrictions
Case 1) Android 6 and above → Call log prompts won't appear if the device has battery-saver ON and if the app is optimised for battery usage when minimized or killed

Case 2) Additionally for Android 9 and above → If the app is restricted for background battery usage (setting named 'Background restriction'), call log prompts won't appear when the app is minimized or killed

For both cases, the user has to disable battery optimization for the mobile app. To do so, mobile app has a setting 'Battery optimization'. 

1. In your mobile app, Tap on the icon on the home screen
   
   
2. Go to Settings > Call preferences > 'Battery optimization'
   
   
3. Redirects to a battery optimization system screen which lists all the applications which are not optimised.
   
   
4. Select 'All apps', go to the mobile app and disable battery optimization.

Note: For some phones, the battery optimization screen with the list of all apps will have toggles. Turn OFF battery optimization for your mobile app

Autostart permission 
Enable the "Auto-start" setting to receive call logs when the app is killed from the recent apps (or) when the app was closed by a consecutive double back press from the mobile app's home-screen. Here’s how you can do the same

1. In your mobile app, tap on the icon on the home screen
   
   
2. Go to Settings > Call preferences > 'Enable autostart permission'
   
   
3. Redirects to a autostart system screen shown below with all the installed applications
   
   
4. Turn on the setting for the mobile app.
   
   

Note: The mobile app offers this customization only for the following third-party OEMs which require the autostart permission → Xiaomi, Vivo, Oppo, Honor, Letv

Permissions specific to Xiaomi devices 
Android 8

Enable the "Start in Background" permission to receive call logs 

1. Launch the mobile app
   
   

2. Tap on the three-dot indicator on the home screen
   
   

3. Settings → Call preferences → 'Battery-saver and other permissions'
   
   

4. Redirects to the page shown below (App info page)
   
   

5. Tap on 'Other permissions and enable 'Start in background'
   
   

Android 9 

Enable "Display pop-up windows while running in the background" permission to receive call logs 

1. Launch the mobile app
   
   

2. Tap on the three-dot indicator on the home screen
   
   

3. Settings → Call preferences → 'Battery-saver and other permissions'
   
   

4. Redirects to the page shown below (App info page)
   
   

5. Tap on 'Other permissions and enable 'Display pop-up windows while running in the background'
   
   

    
Battery saver restrictions ( For Xiaomi devices)

In the app info page, find 'Battery saver' and tap on the same. Choose 'No restrictions'.                                                                         

Android 10 devices (all manufacturers)

"Display over other apps" permission is required for Android 10 devices to bring up call logs. Without this permission, even if the app has all the other usual permissions (telephone and call log), call log cannot be launched. 

The primary setting for Automatic call logs on Android 10 will not be ON until this permission is granted.