No more civiCRM processes

[GuillaumeSorel]

The processes to create a CiviCRM Membership and add an user to a group doesn't work anymore when it used to work previously.
I think upgrading to CiviCRM to 5.35.1 was to turning point but I can't be 100% sure.

To Reproduce
Create a form with CiviCRM processes and try to use it. Each process related to WP works but none of those related to CiviCRM

Expected behavior
Add contact to group and membership to contact

Screenshots
n.a

Desktop (please complete the following information):
MacOS and Windows. Firefox and Chrome/Chromium
CiviCRM 5.35.1 on WP 5.6>5.7 (I've tried to update.)