Guest users not receiving work item notification emails in new Azure DevOps projects

Hello team,

In our Azure DevOps organization, we include at least one guest user, typically the client in each project. We have set up Notifications to automatically send emails when Work Items are edited or updated.

This setup has always worked correctly in our older projects: guest users receive these emails without issue. However, for newer projects created in the last 6-9 months or so, these notifications are no longer sent to guest users. Only our internal users receive the email notifications.

We have verified that the notification rules and the project team configurations are identical between the older and newer projects. The guest users are added in the same way (via Entra ID B2B), and are members of the project with the same access level.

This seems to be a change in behavior or a bug, as nothing in our setup has changed.

Can you please help us identify why notification emails are no longer being sent to guest users in newer projects, and how we can restore this functionality?