question

Check the hardware hash before and after motherboard replacement.

Follow the steps in this guide,
https://docs.microsoft.com/en-us/mem/autopilot/autopilot-mbr

• Deregister the device from Windows Autopilot
  

• Replace the motherboard
  

• Capture a new device ID (4K HH)
  

• Reregister the device with Windows Autopilot
  

• Reset the device
  

• Return the device
  

You probably need open a ticket to MS, but they will require proof of puchase from you for that specific device with serial number.

Repairing Autopilot enrolled devices is complex, as it tries to balance OEM requirements with Windows Autopilot requirements. Specifically, OEM requirements include strict uniqueness across motherboards, MAC addresses, and so on. Windows Autopilot requires strict uniqueness at the hardware hash level for each device to enable successful registration. The hardware hash doesn't always accommodate all the OEM hardware component requirements. So these requirements are sometimes at odds, causing issues with some repair scenarios.
If a motherboard replacement is needed on a Windows Autopilot device, the following process is recommended:
1. Deregister the device from Windows Autopilot
2. Replace the motherboard
3. Capture a new device ID (4K HH)
4. Reregister the device with Windows Autopilot
5. Reset the device
6. Return the device
More reference: https://docs.microsoft.com/en-us/mem/autopilot/autopilot-mbr#deregister-the-autopilot-device-from-the-autopilot-program

If it still doesn’t help, it is possible that the replaced motherboard is registered to other company and haven’t be deregistered yet. You can contact Dell to change motherboard again, or contact MS online support to see if it can change hardware hash at the backend.
Support link: https://docs.microsoft.com/en-us/mem/get-support

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