Before I send my message I first checked all the classic problems:
Plugin content Seblod to the first position
Desactivation of some plugin (Widgekit...)
Test with the template standard protostar.
The problem is still there.
But I finally found the solution after hours of inquiry!
I created a "fulltext" type fields. Section storage "Select to map an existing column" I selected "fulltext".
That's where the bug happens!
Indeed, when I replace "fulltexte" by "introtext [fulltext]" then there is no problem! But In the "select list to map an existing column" there's no "introtext [fulltext]" ! (I wrote"introtext [fulltext]" with my keyboard)
you found a workaround for the way Seblod stores it's data when it comes to introtext and fulltext - those 2 tables are exceptions as Seblod uses them to store it's codes there and since direct usage of introtext/fulltext as storage table is not recommended.