Hi Sergio,
please make sure you are connected and your Moodle is available when accessing the Notifications option.
Please notice that the notifications shown in here are the same that are shown in the following option of Moodle web:
Messages > Recent Notifications
Some push notifications (like messages received) aren't reflected in the notifications table.
If after verifying all this you still think this isn't working, you'll have to check Network requests in the Chrome/Safari inspector and check if the WS call is failing or not (you can use a Pull to refresh to force a WS call).
Kind regards,
Dani