If you are moving users to Microsoft Teams in the destination tenant in waves, are you doing it without setting a Teams coexistence mode for the users who remain in the source tenant?

In a phased BitTitan migration, Teams coexistence mode governs how already-migrated users and not-yet-migrated users can interact across tenants. If you do not plan for coexistence, users who have been moved to the destination tenant can lose the ability to schedule meetings with users still in the source tenant for the duration of the wave period.

In cross-tenant migration scenarios, the coexistence choices are limited. Native cross-tenant Teams federation exists in certain configurations, but it only works when both tenant admins explicitly set it up. Without federation, Teams treats the two populations as separate organizations for meetings and chat, even if both groups still appear to share the same corporate directory during a transitional coexistence state.

From a wave planning perspective, this has a straightforward consequence: groups that schedule frequent cross-team meetings should be migrated together. When you split a team across two waves, you effectively break Teams meeting interoperability between the two halves until the second wave completes.

Have you reviewed Teams meeting dependencies between user populations before finalizing your BitTitan migration wave structure?

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