That's a deeper scientific question that would require careful analysis to answer, provided the software does what it's supposed to. I think it would be interesting to test this system internally though, to verify there are no bugs. Do you mind sending me the input scripts for both the LDA and HSE cases by email?
Note though, that I am not sure there is any particular point in using HSE for this system, it's not making the Au electronic structure better (in fact, maybe worse). It is however still very cool that you can run HSE-NEGF-SOC with full transmission spectrum in 6 hours, don't you agree!