Unable to connect to certain mobile apps on Wifi

I recently purchased the Airtel Xstream Fiber and I notice that some mobile apps which were working flawlessly on the old connection have stopped working. The apps also still work fine when I switch to mobile data. Is there any router setting that needs to be updated?
Can you name those applications and games?
I'm also facing similar issue with few mobile apps like Bigbasket, Paytm and whatsapp.

Whatsapp status won't load when i connected to Airtel fiber wifi. It works on mobile data.

Tried turning off Firewall on Router.

Also changed the dns to Google dns and cloudflare dns on Router > Network > LAN

Tried to change ipv6 dns. But i was unable to change the ipv 6 dns.

Any fix for this?

Is the issue resolved for any of you or still the same?

I also have latency issues for common apps such as WhatsApp. It takes forever to download images or videos within WhatsApp messages.
Turning off WiFi and defaulting to Mobile Internet or switching to ACT Connection will allow me to download the same image or video immediately.
This is very irritating over time and makes me want to leave Airtel. I'm holding onto them because of Airtel One / Black account with Broadband + Landline + Mobile + DTH - all in one solution