Devices show up as unknown join type in InTune all of a sudden.

@Gerardo Sabatino, Thanks for posting in Q&A. From your description, it seems the join type of some devices were changed to unknown all of a sudden. If there's any misunderstanding, feel free to let us know.

To clarify the issue, please check the following information:

1. Please check the "Microsoft Entra Device ID" of one affected device and see if the related device record existing in Microsoft Entra ID.
2. Please check if the device with the same Microsoft Entra Device ID shows correctly with its join type in Microsoft Entra admin center.
3. If the device has any duplicate device record in Microsoft Entra Admin center and Microsoft Intune admin center.
4. Please check if the primary user of the affected device has Microsoft Intune license assigned.
5. Please go to Tenant admin > Tenant status >Service health and message center to see if any related issue there.
6. If we try to go to Settings, Access work access or School, account, info click sync on one affected device, will the status change after waiting for some time.
7. Please check these affected devices to see if there's any difference with the working ones.

Please check the above information and if there's any update, feel free to let us know.

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