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?
There are chance that you may turned on "Restrict background data" option. When its turned on apps don't have access to internet unless you open them.

Go to “Settings“.
Select “Data usage“.
Tap the “Menu” Menu icon icon located at the upper-right corner.
Select “Restrict background data“
Uncheck it to turn it off