But in front glass reflecting black rectangle, it changes its position and size depending on the angle of view.
How can I get rid of the black rectangle?
After doing some research and getting additional information, I have determined that the issue may be related with how the engine handles refraction.
This has been addressed in 4.13 by offering an additional refraction method that can be selected in the material properties. This should help solve visual artifacts like the one you’re experiencing.