There are separation of powers issues with Congress creating administrative courts to determine matters between private individuals.
Congress, in exercising the powers confided to it, may establish 'legislative' courts (as distinguished from 'constitutional courts in which the judicial power conferred by the Constitution can be deposited') which are to form part of the government of territories or of the District of Columbia, or to serve as special tribunals [American Insurance Co. v. Canter, 1 Pet. 511, 26 U. S. 546; Keller v. Potomac Electric Power Co., 261 U. S. 428, 261 U. S. 442-444; Postum Cereal Co. v. California Fig Nut Co., 272 U. S. 693, 272 U. S. 700.] 'to examine and determine various matters, arising between the government and others, which, from their nature, do not require judicial determination and yet are susceptible of it.' But 'the mode of determining matters of this class is completely within congressional control. Congress may reserve to itself the power to decide, may delegate that power to executive officers, or may commit it to judicial tribunals.' Ex parte Bakelite Corporation, 279 U. S. 438, 279 U. S. 451. Familiar illustrations of administrative agencies created for the determination ...