Issue with Azure - Alerts and Action Groups - email notification not received

Looking for advice in relation to our setup in Azure. We have created an Action under our paid subscription but we did not receive an email notification once resolved. Details are below:

1. Actual alerts fired at 12:48 and 15:18 BST on 2 October 2026.
2. History confirms the action group triggered for firing and resolution.
3. The group and verified email receiver are enabled; no muting is configured.
4. Both sample email tests arrived.
5. Actual alert emails remain missing; the first pair were absent from Exchange message trace.
6. Diagnostics incorrectly report no fired alerts.

We have attempted to run through the solution suggested but no joy.

Any ideas?