To prevent the Swoo app from stopping (lock), open the Security app, go to "Boost Speed", click on the cog icon in the upper right corner, then go to "Lock Apps" and select your app/apps there.
Then, in the Security app again, go to Manage Apps, then Permissions and check Background Autostart. Allow Swoo there.
While in Manage Apps, find your app (for example, WhatsApp), tap on it, and under Battery Saver select "No Restrictions".
Finally, while still in the settings for your app, go to App Permissions, scroll down until you find "Pause app activity if unused" and make sure that it's unchecked Reboot and test the app again