a drag&drop object disappears when collides

It's because the paddle has 8-Direction behavior, and objects with 8-Direction behavior can't overlap Solid objects. It doesn't actually disappear, it jumps to the left or right edge of the wall.

If you want to limit the movement of your paddle, you should use an event like this:

Paddle is dragging -> Paddle set Y to clamp(self.y, 100, 600)

They can work together if you are not using them both at the same time, or if you are not dragging your paddle over any solid sprites.

You can add another event - if paddle is dragging, disable 8direction, else enable 8direction