Not all UK citizens received Emergency Alert message in first-ever nationwide test

The UK Government has today conducted its first-ever nationwide test of the Emergency Alert system, which sends emergency, government, and public safety notifications to all smartphone users in the event of danger to life.
As part of the test, every 4G and 5G compatible smartphone in the country was supposed to receive a warning message accompanied with a loud siren-like sound however, it appears that not all citizens received the test message as they were supposed to, with many taking to social media to report the missing message that was due to be delivered at 3pm.
The UK Government is yet to comment on the results of the test.
https://twitter.com/bb9822/status/1650140759230742528
Emergency Alerts will be sent to citizens in the future in the event of severe flooding, fires and extreme weather. The UK Government say Emergency Alert messages will only ever be sent by the emergency services and/or government departments, agencies and public bodies that deal with emergencies.
Emergency Alerts are sent based on the current location of the citizen. The sound and vibration that accompanies the alerts will last for about 10 seconds, even if the device is turned on silent,