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I have just recently bought an Archer C2 as an additional access point to better cover my house besides the main router, Archer C7, handling all the routing, DHCP and other duties. At first i set up the WiFis (both 2,4 GHz and 5 GHz) with same SSIDs and passwords, but with different channels (one router on channel 1, the other on channel 14 for example), as per reccomendation from an IT involved friend. That did work more or less, but after googling i found out the routers support the option of WDS. I enabled WDS on the Archer C2 and all went fine and dandy.

The issue i have now is that the WiFi (2,4 GHz only) works perfectly fine on my father's Nokia Android phone, while it absolutely does not work on my Nexus 5X (regardless of the band). Once WDS is enabled, i get 'Authentication problem' on both bands. Here and there the phone does connect, but the internet performance is spotty - it works for some things (website loading), while it doesn't for other things.

The passwords are set correctly (the moment i will turn off the C2 router, my phone will connect), the distance between the AP and the device is not a problem (my phone is literally 10 cm away from the primary C7 router), both APs (C7 and C2) are connected by a wire (the C2 is also used as a switch), DHCP is disabled on the C2, nothing is plugged into the WAN port, the IP is set to something C7 DHCP server shouldn't issue to other devices, etc.

Any ideas what could be the issue?