I think I have found the root cause for the issue... it was the static IP allotted by airtel which caused this issue.
Airtel had moved to CGNAT and stopped public IPs, because of that port forwarding stopped working for my Homelab servers & VMs due to this I had activated static IP close to a year ago.
now that I have found alternate ways to access my home servers remotely, I decided to deactivate static IP (which airtel charged 300 + GST every month)..
Airtel team deactivated static IP 2 days back and moved my broadband connection back to dynamic which is now CGNAT...
post this, the issues which I had reported seems to be resolved... no more lag or delay in downloads on whatsapp and insta
Note - I will wait for few more days and confirm.