The location of the twist pegs may be causing this to happen. If the lower poles of the tent are secured by the twist pegs a little too far out, a gust of wind or rough opening and closing of the tent can cause the poles to shoot off the pins. You can solve this by moving the twist pegs a little more towards the centre of the tent.
The anchors not being correctly positioned may also cause this to happen. The anchors should be properly located and positioned perpendicularly opposite each other. The experience of thousands of SunnyTent owners all over Europe is that when the tent is correctly installed, and opened and closed carefully and in accordance with the manual, the poles will never shoot off the pins.