Hi.
What is the model number of the Sony Smart TV?
Have you contacted with the supporter of Smart TV to check the problem? If so, what do they suggest?
BTW, you are using Android or iOS Application to access the TV on the mobile phone or computer?

The Model of the Sony TV is HX750
I am using android application Media Remote By Sony Corporation on my Mobile Phone.

This is not a TV Problem because If I connect back my old router everything works fine, Also the Wi-Fi on the smart tv is working perfectly i can access all the internet content on it
It just that mobile application cannot find the tv on the network when i connect through this router.
Also on further checking I have found that I cannot ping the IP of the TV from my computer, but if i ping the ip of the tv from the router diagnostic screen then i get proper reply.
Something is very strange with this model.

stella wrote

Hi.
What is the model number of the Sony Smart TV?
Have you contacted with the supporter of Smart TV to check the problem? If so, what do they suggest?
BTW, you are using Android or iOS Application to access the TV on the mobile phone or computer?

Make sure that IGMP Snooping and multicast are both enabled on the modem.