@MartinBer 

I am seeing the same thiing with an Archer AX1500 in Access Point mode.  I just discovered it yesterday and have not had a chance to troubleshoot.  The WAN port of the AX1500 renews the lease about every 30 seconds.  My DHCP server isc-dhcp-server and is set to a 6 hour lease.  All the other devices on the network honor that lease and renew at 3 hours (50% of lease time). I will post more if I figure anything out.

@MartinBer 

Yes, I have the latest firmware.

@MartinBer Is your device still renewing every 30 seconds?

I changed my TP-Link to a fixed IP address while I troubleshoot another problem.  I noticed the DHCP issue because my TP-Link would randomly reboot every couple days.  Since I changed to a fixed IP address on the AX1500 it has not rebooted.  I have to wait a couple weeks to make sure that the issue is fixed.  If it does fix it, I will contact TP-Link about the fast DHCP renewal because it might be related to the rebooting.

Reference: https://community.tp-link.com/en/business/forum/topic/199292

update: 2020-05-05 DHCP issue does not fix the rebooting. 

After many emails about this AX1500 issue with TP-Link support they stated the DHCP operation is a  "built-in mechanism which is not a bug to be fixed".  They call it "Smart DHCP".  It is the "mechanism that will keep checking if there's another DHCP server here in the period of 30s.The Smart DHCP is to help determine if the router should open AX1500's own DHCP server or not."

@Paul_S 

Now firmware version is 1.09, Im sure you are aware of that