Inconsistent internet access from client WiFi

I'm trying to set up a NETGEAR EX6150v2 as a WiFi extender using relayd, but throughout the whole setup process, the connection to my router's WiFi has been very inconsistent. Most of the time, it just won't work at all (ping returns a bad address). After messing around in the interface and wireless pages, I managed to get it working once (enough to install relayd and luci-proto-relay) but after rebooting my device, the connection stopped working again.

The interfaces I have are as follows: LAN (obviously), WWAN (for wireless connections) and RELAY_BRIDGE, which links the two together. Neither WWAN or RELAY_BRIDGE can pick up an IP address.

I have two wireless radios (for 2.4GHz and 5GHz respectively). Each of them are connected to my router using the scan function. Both of them have a question mark in the Host section (which is apparently the intended behaviour, but is worth mentioning anyway). Both of the WiFi networks match the settings on my router.

So that's my situation. This same problem has occurred with practically every attempt I've had. Any help would be much appreciated.

(Please note: The main router is still on its stock firmware. I can't change anything there, as it's not mine.)

I don’t think you should use both radios to connect to the main router. You may be creating a bridging loop. Choose one band to be the backhaul and use the other as the access point.