Hi jwendeln,
1. Do you configure NAP enforcement with DHCP?
2. Is the DHCP client in the same subnet with the DHCP server? If not, do you configure DHCP relay agent?
3. If you are turning on the firewall, please close the firewall and run ipconfig/release & ipconfig/renew on the computer, then run ipconfig/all to check the result.
If it still couldn't work, please install network monitor the computer, we may capture network traffic to do further troubleshooting.
Network monitor download:
https://www.microsoft.com/en-us/download/details.aspx?id=4865
Best Regards,
Anne
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