Push notifications not working

Expected behaviour

Get a notification on the lock screen or notification.

Actual behaviour

Nothing happens however the notification can be seen after opening the application. Push notifications are on for the app.

Steps to reproduce

1. Run sudo -u www-data php /var/www/nextcloud/occ notification:generate username "This is a test"
2. A push notification should appear but it doesn't

iOS version

iOS 13.3.1

App version

2.25.9.2

Server configuration

Operating system:
Raspbian 10
Web server:
Apache2 but with Nginx reverse proxy.
Database:
MariaDB 10
PHP version:
7.3.14
Nextcloud version: (see Nextcloud admin page)
18.0.1

I have a user with an android device and in my reverse proxy access log I have:
"GET /ocs/v2.php/apps/notifications/api/v2/notifications?format=json HTTP/1.1" 200 834 "-" "Mozilla/5.0 (Android) Nextcloud-android/3.10.1"
This seems to suggest that with the android app it is working fine. This doesn't appear at all for the iOS app.

Start by reproducing the issue with the stated occ notification:generate command on the listed server and iOS setup, then compare the iOS behavior with the Android request shown in the reverse-proxy log. Done means the generated notification appears on the iOS lock screen or as a notification while the app is closed.