@Fergus Brooks, Thanks for posting in Q&A. From your description, it seems the Authenticator app not receiving the notification. Please check on the device side to see if the notification of Microsoft Authentication is opened.
However, if is already opened but can't receive code, please ask admin to open case to involve Microsoft Authenticator support to look into the issue:
https://learn.microsoft.com/en-us/mem/get-support
Or you can call the phone number in your country to see if you can find the Microsoft Authenticator support directly.
Thanks for your understanding.
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