@Max Woosnam Thanks for posting in our Q&A.
For this issue, we appreciate your help to collect some information:
1.Please check if this device doesn't exist both in US intune portal and US Entra ID portal.
2.Did you use autopilot enrollment method to enroll this device to US tenant? If yes, we usually refer to the following link to remove autopilot devices from Intune and Entra ID.
Delete Windows Autopilot Device from Intune, Entra ID
Note: Non-Microsoft link, just for the reference.
If there is anything update, feel free to let us know.
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