2019 Hyundai Nexo SUV FWD

Indicated that there is delay of acceleration on the high driving when I push the gas pedal, it doesn't linearly speed up instead it reduced the speed while I was pushing the gas pedal, worried about the behind car didn't notice the car is slowing due to this issue, it may incur the unexpected accident due to unexpected speed down on the highway driving. Put my car in the dealer to take a look at the issue, they indicated the issue and performed several software upgrade but they failed several times and it still didn't get fixed yet. I also heard that it has orange warning message which need to replace hydrogen related coolant must be replaced but they don't have parts to replace it immediately. There is no actual incident so far, but worrying about this unexpected delay of acceleration, and unexpected speed down could cause the accident. But they cannot figure it so far, been 4months.

WHEN THE CAR IS MOVING, A "REGENERATIVE BRAKE SYSTEM FAILURE" MAY OCCUR. WHEN THIS ERROR OCCURS, BRAKING EFFECTIVENESS IS DRAMATICALLY REDUCED AND THE CAR'S SPEED IS LIMITED TO 13 MPH. ADDITIONALLY, THE CAR WILL NOT CREEP FORWARD OR HOLD POSITION WHEN THE BRAKE IS RELEASED, POTENTIALLY ALLOWING THE CAR TO ROLL BACKWARD WHEN THE BRAKE IS NOT APPLIED. THE FAILURE OCCURS MOST COMMONLY WHEN THE CAR IS CREEPING FORWARD IN TRAFFIC, BUT CAN ALSO OCCUR AT FREEWAY SPEEDS. TURNING OFF THE CAR, RESTARTING IT, AND PULLING FORWARD - IN THAT ORDER - WILL CLEAR THE BRAKE FAILURE WARNING LIGHTS AND RETURN THE CAR TO NORMAL OPERATION UNTIL THE NEXT FAILURE. TIME BETWEEN FAILURES CAN BE AS LITTLE AS A FEW MINUTES AND AS GREAT AS A FEW DAYS. THE FAILURE SETS DTCS IN THE VEHICLE ECM BUT THESE CODES HAVE NOT BEEN SUFFICIENT FOR TECHNICIANS TO IDENTIFY THE FAULTY COMPONENTS. THE VEHICLE WAS RETURNED TO CUSTOMER WITHOUT THE TECHNICIANS OBSERVING THE FAILURE OR PERFORMING ANY FIX. THE CAR THEN FAILED AGAIN A FEW DAYS LATER AND HAS BEEN RETURNED TO THE DEALER FOR FURTHER ASSESSMENT.