unable to edit the existing Approval Rule

When I want to modify the existing Approval Rule so I change the End Date field ,that changed to a date before the current date. Then the system does not allow saving due to the following error: "Row 1: Please enter value(s) for: Approver." After, I fill approver and save the field is blank. It doesn't save approver.

When I am trying to create a new Approval Rule with a higher priority than the existing one, the system does not allow it and displays the following error: "An approval rule with the same combination of some or all criteria field values within the specified date range already exists. Update the criteria or date range to create a unique rule. For more information, read the guidelines in the Creating Approval Rules topic in the Help Center."