Is there another approach to get the background running infinit and smooth from right to left other than the bullet beheaviour?
I had similar performance issues in an endless runner I made with the Bullet behaviour, so I replaced Bullet with setting the X position using the lerp function e.g. Set X to lerp(Self.X, Self.X - Speed, dt), where Speed is a Global Variable set to the same speed as the Bullet.
Here's the built-in Auto-Runner example, but modified using lerp:
capx r233