Right, for the rotation to work correctly, the front of the object needs to be aligned with the scene Y axis (face towards the positive values of the Y axis). To check the axis orientation in Shapespark, you can select any light or a light probe in Shapespark editor and it will show the scene Y axis in green.
As you discovered, if for example a back of a single sided 2D surface is facing the positive values of the Y axis, this invisible back will be rotated to always face the camera, and the object will be always invisible.