Apps on Android devices may not always run stably in the background for various reasons, which may differ depending on the device model. This is most often due to Android OS optimization function, or so called "battery save mode". In such cases, the system closes apps in order to reduce the load and free up RAM.
If AdGuard VPN is disabled on your device, your personal data will become vulnerable. To avoid such problem, you need to open this link and follow the instructions for your device with one difference: wherever it is required, choose AdGuard VPN instead of AdGuard.