Many notifications show up when connected to WiFi

I have Moto G (2nd gen) with 3G connection. During my office hours I am constantly conncted to my 3G network and when I am to my home I connect to my WiFi network. I have noticed this unusual behavior for past 2-3 weeks. When I go home and connect to my home WiFi network many notifications start showing up - like notifications from apps like MakeMyTrip/Flipkart/Yatra and more. These notifications do not show up on my 3G network. It seems these **pending** notifications only show up when connected to WiFi. Notifications for apps like WhatsApp/Twitter work fine of 3G network. What would be the reason for this and where I should be looking if I want to resolve this issue?