Just thought I would chime in here too. I have exactly the same issue with a WPA7617 and as yet have found no way to fix it. Absolutely insane that there is no setting in the webconfig to disable the DHCP.

@Draconos 

absolutely true. I just don't get it. In the end I gave the powerline adapter a fixed ip address (that was mentioned as one of the work arounds here on this forum). Have yet to find out if it helps. Had no outages since that change.  

@Martin010 Unfortunately it doesn't work. For me anyway.. I set mine to static out of the box due to how my networks setup, and its failed countless times since. Hopefully you have better luck.

So, after sending a rather impolite email to the support line, I was supplied with this link to a seemingly beta firmware for the WPA7617 with instructions to install it and set my ip to static.. Havent had it long enough to know if its solved it or not but if anyone else comes along with the same issue for the 7617 maybe try this

https://static.tp-link.com/beta/2021/202105/20210511/TL-WPA7617(EU)_V1.zip

Just to add that I am also facing this issue.

I have two 7617 powerline extenders, one in the house and one in my shed.

Both set to use static IPs, the one in my house never starts the DHCP server as it always has good connectivity with the powerline adapter/powerline network.

The one in my shed disconnects from the powerline network every now and then for a few seconds before connecting again.

However, whenever it disconnects, the extender starts the DHCP server immediately, thus kicking me off the extender and reconnecting me without internet.

Then it stops the DHCP server when it reconnects to the powerline network and my device needs to be reconnected again to the extender.

Like many others, I would rather the extender not use a DHCP server at all as this simply prolongs the time my device has no internet.

Looking at that firmware file you posted @Draconos, my device came with that version pre-installed.

Update on this matter;

I had some power issues last week at home, causing the Main TP-Link Deco to be without power for a while. When everything was restored again, I noticed my Deco system started using a different IP network again. So even with the TL-WPA on a static IP, it still threw everything out of order.

I really hope the firmware will be available soon so this can get fixed once and for all.