Hi @gmtoz, please proceed with the following:
1. Turn off DHCP on the VR1600v .
a. Navigate to Advanced -> Network -> LAN settings
b. Untick DHCP Enable
c. Click Save
2. Configure a static IP on the Airport express in the 192.168.1.10-192.168.50 range
3. Configure the static IP of the Airport express in the DMZ of the VR1600v
4. Ensure the WiFi SSID of the Airport express is different to the VR1600v SSID
Let us know if we can be of further assistance. Thank you.
This more or less worked as it now relies on the Apple Airport Extreme to do the DHCP routing and also removes the conflicting DHCP routers (regardless of whether TP-Link DHCP is on or off I found). DMZ setting seemed to be key.
It's not ideal for me as I can no longer use the ethernet ports on the TP-Link (due to being on a different network it messes up LAN traffic) and so I have to add an extra hub in for my ethernet ports. What it does prove is that the TP-Link is a very poor DHCP server as the Apple works so much quicker.
None-the-less it will work long enough for me to switch to a provider that uses quality routers.
I have expericeing the same DHCP leasing issue, I wonder if my modem is on the latest version that might have rectified this issue.
FW: 1.1.0 0.9.1 v5006.0 Build 180828 Rel.35294n
HW: Archer VR1600v v1 00000000