If they are updating something.... Why is there Always a problem on wp phones? Updates on android or IOS, no problems... Even updates on a symbianphone (my old phone) no problems at all... Come on @whatsapp... Do something about it!
I also have this problem. My brother has the Lumia 820 running Windows Phone 8.0 and his notifications are absolutely fine. I have the Lumia 920 running Windows Phone 8.1 and now my notification are arriving very late or not at all. This has only happened recently. I wasn't sure if it's because I was changing some settings or if it's a whatsapp issue.
Funny, I seem to have the opposite problem. I have turned off WA in the background (and this has hugely improved my battery life) but occasionally today I have actually received notifications! So the OS is not stopping WA from running in the background...
And when it is in the foreground, WA is a HUGE battery drain (approximately 0.5% per minute).