Oracle CX Sales - Predefined Object Sharing Rules is not working

Summary:
Hi all,

We're running into a permission error that doesn't seem to be resolved by data access changes, and we'd appreciate some guidance on which role/privilege actually governs this.

Issue:
A Sales Representative gets the following error when trying to update the Organization Name and other fields on an Account record created by other user:

You don't have the required permission. You can request that your help desk change your security settings. Contact your help desk. (FND-14)
Application Name: ORA_CRM_SERVICESAPP

Steps already taken:

1. Confirmed the user has Full access via the "All Accounts" object sharing rule (Navigator → Tools → Sales and Service Access Management → Object Rules → Account →