Bravia and Android phones keep losing internet connection while still connected to wifi, laptops OK!

We use a COX internet connection.

This seems like a router configuration problem. The android devices including Sony Bravia, phones and Amazon Alexa keep dropping internet connection intermittently while remaining connected to wifi all the time.

The laptops work fine but same thing happens on windows( very rarely though ), it's very frequent on Android TV (Bravia) and android phones, very rare on iPhones too.

I changed the IP settings from DHCP to static in my Droid and the phone connected to internet instantly and stayed connected till now. This seems to solve the problem.

I've also reserved IP to all these devices in the LAN setup of router configuration which seemed to solve the problem at first for all the devices but the Droid dropped internet again after few hours, this time for longer period. I'm also using google DNS and even dynamic DNS doesn't solve the problem.

We have lot of devices at home and I want to fix this thing on the router level, so that we dont face the problems again and again.

Also the 5ghz connection seems to be very unstable, TV keeps dropping it frequently and router is 4 feet from it. It kinda became stable after I changed channel to 36 and reserved the IPs.

I hope somebody understands the problem and provides me a permanent fix.

This thing is getting too annoying and wasting lot of my time.