Why are there blue boxes with a question mark?

Question

Java

Hello everyone, please tell me why blue squares with a question mark appear in WebView?
It seems that it is formed where it is empty. And how to fix it?
Application structure:
The main window of the activity is inherited from TabActivity, each tab through intent opens classes that are inherited from the AppCompactActivity class, and creates a ViewPager that is attached to the ActionBar, ViewPager using fragments adds other classes that open WebView .

Answer 1

perhaps there should be an image, but the program cannot find it