We have an attribute on the Contact record that is required. When a Contact which is missing the required data in this attribute is added to an Opportunity, the system does not provide an error code. Therefore, the users keeps added the data in the Opportunity. When they save the Opportunity record, the user is presented with an error code.
[CR Error: There are empty required attributes: 'Department']
NOTE: "Department" is the name of our custom attribute in the Contact record.
Even if the user removes the Contact from the Opportunity, they still cannot save the record and lose all there data entry time.
Below are two recommendations to resolve this;