A 4th Mitsubishi MRJ90 test aircraft, JA23MJ, scheduled to fly from Honolulu International to the continental United States and join its siblings undergoing certification testing at Moses Lake, Washington, had to return to the airport shortly after departure on Thursday morning. The reason for the diversion is inaudible in publicly available ATC recordings, but the pilots request to stop climb at 9,000 and return to the field. The first MRJ90 to come to the US for testing in the summer of 2016 had to turn back on its first attempt after having issues with an air conditioning system.
Source: avwebMitsubishi Regional Jet Struggles to Join Siblings in Washington