Hi @Jennifer,
First,please verify:
- If the guests are added in Microsoft 365 group. If not, here are the articles about adding guests to Microsoft 365 group: Add guests to a Microsoft 365 group from the admin center.
Second, if the guest was invited from SharePoint in Microsoft 365 and Azure Active Directory B2B.
Please follow this article to configure issue in your directory: Guest doesn't receive group email conversations.
Third, if the problem persists, please follow this article to review the steps you took to add guests and if you missed something. I suggest you try these steps on a new site. Change your browser or computer, add these guests on another site, and see if they get an email notifications/invitations.
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