Problem of access to the body field with a simple post

A curious thing. I'm an admin with all the rights. I disabled the permission module but on some posts I have the body field with the mention : 

"This field has been disabled because you don't have sufficient rights to modify it."

With articles of the same type (post) I don't have this problem. I looked in the field body the permissions, the possible options and also in the database. I don't see anything. It's quite strange! 

The articles were imported, I didn't create them. 

Have you ever seen that? How can this be explained?

PS : With a custom theme and Backdrop CMS 13.4.2 and php 8.4