first try to relate this to specific hardware.
The client handles the DHCP request.
some drivers want to renew/reuse a previously obtained IP-address and DO NOT request a new one.
and they ignore the NACK received from the DHCP server.
-> here the driver needs update or you need manually release/renew the address.
second check your DHCP server logs, it may be the DHCP server receives the request and returns the response, but for any reason the respons is not sent over the wifi to the client, this will need further troubleshooting.