Let me guess, you are using it with a flip cover right?
That is the screen that appears when the flip cover is closed. It is intended for flip cover with clock face like this
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but doenst matter what kind of flip cover was used, it will still trigger if closed
Its most probably when the flip cover is flipped fully backward, the magnet(or something, not really sure) inside the flip cover triggered something inside the fonepad and the fonepad though that the it was closed.