Check on your phone with a wifi analyzer app the wifi channels in your region. Maybe that is the problem. Change the wifi channel of your router. I have C5 v4 too, and it works really nice! No problems with the wifi.
Your other problem, related to throwing net, is not the routers fault. It's your ISP. The connection is stable, speed is fast and stable too. I have a PPPoE connection.

BUT I have a real problem, what is the routers fault. Delayed IPv6 address allocation. Without the router, I get IP after a few seconds, but with the router, this is delayed. It takes exact 3 minutes to get the IPv6. I have to wait to appear in IPv6 section for the default gateway address The ip4 one appears instantly, but ip6 version of itt no.. Only after that I get my IP6. Why it takes so "long"?