mobile

I have a bit of problem here android experts. I'm using WhatsApp and recently I started noticing that I only receive the messages when I open the app. If the app is running in background (i.e., not removed from recents screen) then i keep getting the notifications. Once i clear the app from recents screen, then i don't get the notifications unless and until I open the app or go to Settings > Accounts and Sync and manually Sync WhatsApp. I have tried everything from re-installing WhatsApp and clearing the cache and data and also no task killer applications is stopping WhatsApp from running in the background. And even though I don't receive the messages, the WhatsApp service keeps running in the background. I tried sending a message from my friends phone and didn't receive the message but when i checked under Settings > Apps > Running, it showed WhatsApp is running One process and One service. I hard resetted my phone also but nothing happens. Please give me some solution to this problem. The notifications arrive on all other apps except for WhatsApp.

I have checked previous threads on XDA and none seem to solve my problem so I'm posting a new thread