That's really odd, @Bam, and in theory , impossible! How do you switch your data and WiFi off? Is this through the main 'Settings' app of your phone, or by using the pull down quick settings menu from the top of the phone?
i was wondering if i was imagining it! i turn them off by the pull down quick settings menu from the top of the phone and to avoid interruptions i've turned on "do not disturb" between the hours of 23:00 - 06:00. After 6am even before i've turned WI-FI and mobile data back on the notifications start coming through but i can't view them as it says "not connected" as i would expect.