It's me again !
'Seems [to me] that all is fixed.
I don't understand what exactly happened: this night I added a few books to Calibre library and, as fetching Mediapart news is an automated process here, it started during this time.
When it was over I couldn't resist to have a glance at the resulting epub.
I wad totally surprised when I realized that ... yes, the articles where all complete !
I just noticed that images where not there (only an icon of file) :/, but that was the night: not the moment to debug, rather sleeping time.
Today, I wanted to resume all of this, then I started in fetching another epub of more up-to-date articles ('Mediapart' news are updated 3 times a day) and then ... images were there, in this new epub ! :O
Not sure of what really happened here [I tested another once with 'ebook-convert' ==> same "paywall issue" with the last fix by Kovid ('Update Mediapart ')], but for these threads, I think one can consider it as "SOLVED".
Again a great « Merciiii ! » to Kovid for his help at the beginning, solving many issues induced -- I infer -- by the olderness of the recipe. That was a good start.
And also thxs to all those who red these, trying to see if they could help.
And, lastly, sorry for my English.