No objection that has not been urged before the board, its member, agent, or agency shall be considered by the court, unless the failure or neglect to urge the objection is excused because of extraordinary circumstances. The findings of the board as to the facts, if supported by evidence, shall be conclusive. If either party applies to the court for leave to adduce additional evidence and shows to the satisfaction of the court that the additional evidence is material and that there were reasonable grounds for failure to adduce the evidence in the hearing before the board, its member, agent, or agency, the court may order the additional evidence to be taken before the board, its member, agent, or agency, and to be made a part of the transcript. The board may modify its finding as to the facts, or make new findings, by reason of additional evidence so taken and filed, and it shall file the modified or new findings, that, if supported by evidence, shall be conclusive, and shall file its recommendations, if any, for the modification or setting aside of its original order.