One of the useful features found on Xiaomi devices is the ability to set "Autostart" permissions for each app. This allows the device to extend its battery life when an app is not in use. However, the tradeoff is that you may be missing out on some push notifications if you have closed the Xplor app. To rectify this, you will need to allow Xplor to be on the exception list for Autostart.
To do this, launch the Security app from the home screen
Tap on Autostart > Permissions > OK
Check that Xplor is enabled. This will ensure that the app is whitelisted and is allowed to autostart again even if it is closed.