Hi,

try to update any module (e.g. Sales or CRM) or, preferably, the 'base' module through the interface. It will force the regeneration of the view. Sometimes, installing or uninstalling modules might break this very special XML representation. Simple updating should help.

Also, this app - https://apps.odoo.com/apps/modules/17.0/security_user_roles/ - might be a good helper when you have many users.