The most likely answer is that you have placed an unregistered Credit Card, points card, access card that has a scanning tag too close to the back of your phone. The most likely way of this happening is if you have a flip case with cards in it. So whenever you open your phone the flip part of the case with scanning cards in it sits at the back of the phone, your NFC within your phone detects the card but as it has not been registered on your phone(because it’s a frequent flyers point card, library card, public transport card etc) then a message will pop up stating “No supported application for this NFC tag”. You can replicate this problem by rubbing the back of your phone against all your cards in your purse or wallet!!