@Sunshine Ok so, Just a single device gets disconnected from the router, rest all devices are still connected and works fine.

Update: the device automatically gets connected by itself , if not connected manually within 4-5 minutes.

let me go with setting up the DNS server manually, previously it was setup dynamically by ISP as IP ADDRESS : 103... something.

  @Sunshine Now the disconnecting and reconnection issue is happening with other devices as well. 
Here's what I did:

Firstly I Contacted the Customer Support of TP link , and here's what they suggested to do:

i. Changed 2.4g channel: 11 and channel width: 40mhz

ii. Changed 5g channel: 36 and channel width: 20-40-80mhz

iii. Changed mtu size : 1400

iv. Added Primary dns to 8.8.8.8 and secondary dns as 8.8.4.4 (in the DHCP settings)

The Person told to replace the product if issue still persists. and the issue was there

I got the replacement from the E commerce from where I purchased the product. And to I got the same issue with a new device as well.

  @Maroof_ 

  @Maroof_ I am having the exact same issue as you with my router. Have you received any information on a possible fix? Not looking forward to buying a new router

  @Maroof_ 

I also have the same issue. Any update to your problem?

  @Stealthfatal 

Did you fix the issue? I'm having trouble he same problem.