Validation rule on Hire Flow for assignment dff segment firing incorrectly

Summary:

We have a Validation rule created on various Update employment flows to validate a DFF segment is 8 numeric characters. It is a simple RegExp check. This works fine on Update flows (Change Assignment, Correct Employment, Local Global Transfer), but it is firing too early on the Hire flow before we even get to the section to put a value in the field.

Content (please ensure you mask any confidential information):

We created the below Validation rule and it works fine on all our update employment processes. However when we try to create the same validation on the Hire flow it is firing too early and appearing as we click to go to the Assignment section. That is not correct, it should be checking the value we enter into the field and then firing after we leave the field on the assignment section.