Outlook Mail Received trigger doesn't poll, only works manually or after re-activating workflow

I have a workflow on n8n.cloud, that starts from an outlook mail received trigger. I have configured this to poll every 30 minutes, for mail in a specific folder. This is the only trigger in the workflow. The workflow is saved and made active, no errors are flagged.

The outlook (microsoft 365) has been signed in and a credential has been created OK, I can test the workflow manually and it works fine but nothing happens if it’s active, the only way I can “nudge” it is to edit+save the workflow, or make it inactive/active again, then it will detect mail and start a new execution right away.

This is what does and doesn’t trigger the workflow:
:cross_mark: New mail comes in and we wait for polling
:white_check_mark: Manually execute the trigger
:white_check_mark: Edit the workflow (even just moving a node) then saving
:white_check_mark: Make the workflow inactive then active again.

Also, when it does execute, it may only find 2-3 emails when there are many more available.

If it makes a difference, I’m using the Brave browser, shields are down, not that it should matter since this would be running server side.

On the Azure side, I can see successful entries on the Sign-In Events page. I’m not sure where I’d find mail subscriptions, couldn’t see it in the Graph Explorer under GET /subscriptions.

What could possibly be wrong? I don’t understand why it works manually but not as an active workflow.

Thanks