Participation Date Changes After Open Enrollment

We have about 10 employees that had their participation date change after open enrollment was processed for 2017.  There were no assignment record changes that we can see with these employees.  No idea why these dates would have changed.

When processing 2018 OE the dates did not change so they still reflect Jan 2017.  What is there about this record that would have caused this to change for the last open?  Is there a clean way to get that back to the correct participation date of Jul 2014?

The first screen shot shows correctly.

The second one shows where the date changes after 2017 Open Enrollment.