It seems like you've covered several troubleshooting steps already. Since the issue persists, consider checking if there are any conflicting configurations in your network, such as duplicate IP addresses or conflicting DHCP settings on other devices. Additionally, ensure that the DHCP server has proper permissions.
You might also want to restart the DHCP server service to see if it resolves the problem. If the issue persists, reviewing recent system and DHCP server logs for any relevant error messages could provide additional insights into the problem.
Lastly, consider temporarily expanding the DHCP scope range to see if the problem persists with a broader range of IP addresses. This could help narrow down whether the issue is specific to the current scope or a more general DHCP configuration problem.