Unless such appeal is withdrawn, a referee shall promptly hear the claim, de novo, and render a decision thereon. Unless a party has waived the notice or agreed to a shorter period of time, notice, by mail or otherwise, of the time and place of such hearing shall be given each interested party not less than five days prior to the date appointed therefor. The parties, including the administrator, shall be notified of the referee’s decision, which notification shall be accompanied by a finding of the facts and the conclusions of law upon which the decision is based. The referee may, for good cause, issue a decision which remands the case to the administrator for such further proceedings as the referee may reasonably direct. Such hearing shall be held by the referee designated by the chief referee. No referee shall hear an appeal if he or she has any interest in the proceeding or in the business of any party to the proceeding. A challenge to the interest of a referee may be made by any party to the proceeding. The decision on said challenge shall be made by the chairman of the board, after proceedings held in accordance with such rules of procedures as the board may establish.