2019 HYUNDAI NEXO Unknown Or Other Problems

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...