@superyorch Hello 

 TP-Link Range extender working as a proxy will replace each of its clients’ MAC address with a virtual MAC address generated automatically by Range Extender. Thus the router will take the virtual MAC address of the clients as their real MAC address, currently there isn't a way to turn off the proxy mode. You could learn details from this related FAQ 

How to set up Mac Filtering on router (blue UI) to control the devices connected to the Range Extender?

If you wish to set up Mac filtering or access control on router through RE, here are some  instructions & FAQ that may help. 

- Disable Mac filtering/ Access Control feature on your router 
- Turn ON the extender and connect all the Wi-Fi devices to your extender network.
- Login Range extender web page and find the *virtual Mac of your devices as FAQ above
- Go to router web and add 1) RE 's mac 2) ALL the Mac address beginning with RE's Mac addresses on router Mac filter/ access control list 
e.g. If RE Mac is 50:C7:BF:1B:ED:C6, add all the Mac addresses  with 50:C7:BF into router settings

( for dual-band range extender: add both RE's 2.4GHz & 5Ghz Mac addresses 
How to find Mac of WiFi work: on Windows computer, open cmd window, put in  netsh wlan show interfaces. The BSSID is the Mac address of your Wi-Fi network )

Hope this helps. 

Hello @superyorch 

Thank you for sharing the case details. 

1-  I wonder if manually set up a static IP on client/ device itself helps :  e.g. set up static IP for Windows/IOS/MAC etc.  
Here is a guide to set up static IP on Windows: https://www.tp-link.com/support/faq/41/

2. Try to reserve an IP address on router using Virtual MAC address on RE web client list  for clients that connected to RE and works at a fixed location ( does not need to roam between Router and RE, this may not work for mobile devices that need always roam between RE and router. )