Block editor: content resets to the previous state in "Edit as HTML" by clicking somewhere outside of the editing window

When I'm adding my custom block and then trying to edit it in "Edit as HTML" mode, any changes reset to the previous state every time when I click outside the editing window. Let say default HTML in my block is div class="wp-block-my-custom-video-box"/div, if I make some changes, let say div class="wp-block-my-custom-video-box"some text/div some text will disappear. This issue related to WordPress ver. 5.3.2, with ver. 5.2.5 everything works fine. Help me figure out, please, what can cause such strange behavior?

this is a simplified example of the component: https://pastebin.com/RqQP0LCM