Portfolio Epic's inProgressDate API property is not updated to reflect the most recent transition to "In Progress" status

Issue Summary

This was discovered while testing for, and is somewhat related to JIRAALIGN-4861.  If an Epic is moved to "In Progress" by a child Story, the inProgressDate is recorded (though incomplete). 

If the parent Epic is then manually changed back to "Not Started", and then later changed to "In Progress" again by a child Story, the inProgressDate API property does not get updated. The property still shows the original date of the Epic's first transition to "In Progress".

Steps to Reproduce

1. Find a new Epic that has child Features and Stories, but nothing is "In Progress" yet.
2. Change one of the child Stories to "In Progress" and verify the parent Epic moves to "In Progress" automatically.
3. Do an API GET on the Epic ID from step 1. Make a note of the inProgressDate property.
4. Manually set the Epic back to "Not Started". Check the inProgressDate property and note that it has not been cleared and set back to null
5. Change another child Story to "In Progress" and again verify the parent Epic moves to "In Progress" automatically.
6. Do an API GET on the Epic ID. Make a note of the inProgressDate property.

Expected Results

Epic's inProgressDate API property should be updated to reflect the most recent transition to "In Progress".

Actual Results

Epic's inProgressDate API property is only set on the initial transition to "In Progress" and fails to update on subsequent transitions to "In Progress"

As with JIRAALIGN-4861, the in progress date captured by epic export is correct.  The date returned by the API is incorrect.

Workaround

No known workaround.  The dates are set correctly if the Epic is set to "in progress" manually in the UI, but this isn't a feasible workaround.