Can you login the admin interface of the modem when it freezes? Any error on Status screen?

it sounds like wrong physical connection. The WAN port on the C7 should not be used any more if you want to use it as access point. No need to configure WAN IP address either. Connect the LAN port of...

How do you connect the VoIP phone to the router, via Ethernet or WiFi? What kind of protocol does it use? Maybe there is compatibility issue? You can confirm with tplink technical support

On the back label, next to the model, you will see (US) or (EU). Also you can compare your firmware version with the US website or an EU country website, see if the firmware of your extender belongs...

Maybe they still need time, and I think it's fine to use wifi backhaul

I don't think so. janoost wrote Question: would it be possible to downgrade firmware on the deco m5?