If the same person is an approver in two consecutive stages and they approve in the stage before (they might not have approved if set up with 'one to approve' rule but another person approved), the system will assume that person does not need to approve the form again as they already approved the form into the stage.

In this case, if there is more than one approver in the new stage, all approvers who did not approve in the stage before will have a blue approve button, but the person who already approved in the stage before will not have this button.