There was an issue: #1954968: Required CKEditor fields always fail HTML5 validation
"An invalid form control with name='{name}' is not focusable" JS error is thrown when a textarea has "required" attribute, but is not visible.
This was fixed in CKEditor: https://dev.ckeditor.com/ticket/8031
Now CKEditor removes the "required" attribute from textarea during initialization.
But the problem still exist if the "required" attribute is added via #states.