wp-admin redirection when adding a new post

Hi,
It’s been a while since I seek without finding a solution.
I installed a multisite and the plugin domain mapping.

See the procedure:

– I login in with super admin in: https://mywebsite.com/wp-admin
– I go to a child website admin: https://mywebsite.com/fr/wp-admin
– I add a new page : https://mywebsite.com/fr/wp-admin/edit.php?post_type=page
– I click on publish.
– I’m redirected to: https://mywebsite.com/wp-admin/post.php?post=20&action=edit
– My permalink is : https://mywebsite.com/new/ INSTEAD of https://mywebsite.com/fr/new/
– When I go to https://mywebsite.com/fr/, I have a 404 page ??
All pages are on https://mywebsite.com/

What I do wrong?
Do you have so ideas for me?