Some sprites are not rendered in triangular area

Some sprites in a triangular area are not rendered as shown in the attachment. Even though the background is also a sprite, it is rendered correctly. I can't test it on my devices since this problem doesn't occur on our devices. But many of our players reported that problem. What can be the reason for this?

Thank you

 

The problem was that the background and the other sprites were on the same z. Strangely it was working fine on most devices. Don't forget to check z values in case you encounter this problem.