Hi @Nebur692 

Thanks for posting in our business forum.

Don't know what kind of device that is.

So, refer to this first: How Does DHCP Work? Common Questions and Solutions

You probably need a new DHCP discovery to work. Usually, reboot the client would do it. But if it does not, it means the client does not actively request a new IP address(discovery) after the reboot. It is strange.

If you need to find out the reason why, we need to Wirehshark and find out if it is either your client does not request the new IP or it is the router did not respond with the new IP.

How to capture packets using Wireshark on SMB router or switch

How to Use Port Mirror to Capture Packets in the Controller

Hi  @Nebur692 

I wrought about this bug 5 years ago. I found it in er6120, er605.

The problem is not stable, may be 50/50%

If to change MAC for some user in the reservation table - in 50% of cases user will not get it!

ONLY after router been restarted. But in another 50% cases everything will be allright.

here is this bug I reported for 8411: https://community.tp-link.com/en/business/forum/topic/703686