Properly integration of Zyxel AX7501-B0 and NWA210AX

Hello
I've the two above mentioned Zyxel devices and several times per day my internet connection (fibre) is very slow, so that applications like video-calls or web-radio are interrupted. I want to ensure that I've a good / valid setup chosen and that the issue for the problems is not related to my configuration. Below the key aspects of my setup:
  • The AX7501-B0 is connected to the fibre and is located in my cellar in the ground floor. Here I've a WLAN GROUND_FLOOR created.
  • The AX7501-B0 is connected to the NWA210AX via a 1 GB LAN cable. The NWA210AX is located in the first floor and creates a second WLAN FIRST_FLOOR.
  • This setup works generally and I have from a signal perspective a small overlap between the two different WLAN networks.
  • The overall IP range for the AX7501-B0 is 255 (devices) and both WLAN networks are able to hand-out new IPs of the same range. There exists therefore a small risk that the same IP might be given to two devices at the same time. 
For me is not clear how I could configure with the two devices only one network like WLAN FAMILY and the NWA210AX would just repeat the WLAN (over the LAN capable).

Any thoughts are highly welcome.

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