Push notifications problem after OTA upgrade to Marshmallow - KIWL24

Hi, I'm experiencing problems with push notifications after upgrading to Marshmallow using OTA update. Basically most of the time, when the screen is turned off, I don't receive any notifications (whatsapp, gmail, etc.). When I open the app (for example, whatsapp) then I receive all the old messages for which I did not receive any notification... is anybody experiencing something like this?

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