I have the same issue, I have linked the employee and partner but still facing the same issue.
the issue occur accidentally today.

Hi Monawar Sufian,

Could you please verify whether the user has been granted the appropriate access rights? Additionally, ensure that they have access to the necessary contacts (res.partner).

If the issue persists, kindly provide more details, such as the specific access rights assigned to the user and the access rules currently in place for them.

Thank you.