Why is the graphics being erased?

Question

Java

There is a class for working with JPanel, through which I insert a background image into it and draw with the mouse. The picture in any case is static and is not erased when scrolling or collapsing. Graphics drawn with the mouse are erased. What could be the problem?
paste.ofcode.org/33vxubjb5nzf2ghYtynk6py