What you're observing is accurate behavior. When a user logs in to the SSO portal (via Entra ID) for the first time, Meraki SM captures that user's group membership from Entra and creates a dynamic tag based on that, but, users who never log in to the SSO portal do not sync automatically. Their group memberships aren't pulled into SM until they authenticate at least once.
As mentioned you can try using Meraki API combined with Microsoft Graph API to extract Entra group membership and apply corresponding tags to devices in SM via API.
I am not a Cisco Meraki employee. My suggestions are based on documentation of Meraki best practices and day-to-day experience.
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