Why are Drupal classes being removed??

Question

Drupal

Hello!
Can you please tell me why the classes are removed in the Drupal Panels module, Bootstrap theme?
I add content, prescribe classes, everything is fine at first, and then the next time the content is edited, the classes are deleted, I also noticed that the span also disappears. Also, next time I go to CKeditor, the classes are not visible at all. What could be the problem?
Thank you in advance!

Answer 1

It is necessary to set valid tags both in CKeditor itself and in text formats (problem due to code filtering)