Object Validation Rule not working as expected - 23C

Summary:

We have an object validation rule that prompts error message if a DFF field is null or if the value in that DFF field is not equal to the grade field.

This rule is only for Edit Offer and Create Offer actions in Recruiting. When we enter the assignment section for the first time, populate values, leave the DFF field to null, then proceed to the next section, the rule is not triggered upon exit. If we go back and exit the the section again, the rule is then triggered and validation error is prompted.

Content (required):

rule snippet below. we used EMP_Groovy_OfferMode to triggered the rule in EditOffer and CreateOffer page.