Two app windows open on home screen and can't close them.

I have an LG G4 running marshmallow 6. My problem is two app's, Messenger & messaging, have windows open on my home screen, and I can't get rid of them? When I click on the cross, they don't close, and if I try to slide them to the side, they won't go. I've tried re-starting the phone, but they are still there? I can see a button at the bottom of the screen which says 'clear all', but nothing happens when I try to press it, as if it's greyed out. I can send a screen shot, if that helps?

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