Getting the same problem, even why using sudo().

Did you find the solutions?

In Odoo, the CRM module includes a feature for managing leads, which are potential customers or sales opportunities. To secure the leads in Odoo, you can set up access controls on the CRM leads and related data. This can include setting up user roles and permissions for who can view, create, and edit leads, as well as setting up security rules to restrict access to certain leads based on certain criteria.

For example, you could set up a rule that only allows sales managers to access leads with a certain level of potential revenue, while only allowing sales representatives to access leads that have been assigned to them. Additionally, you can also use the Odoo access control system to restrict access to certain fields on the lead form, such as contact information or budget information, to only certain users or user groups

Did you activate/select the correct company in top right corner. If a company is not activated it gives you similar error messages.

I think you have multi company so make sure to grant admin access to all companies. because there is some contacts linked to sales team for another company. You can go to user form and add all companies in "Allowed companies" field  for admin user.