"FIM tells me that this message will present itself whenever HPSOV is not closed when it has been commanded to close."
Beeline: "If the servo muscle air cannot be ported to ambient it will keep the valve open."
Your statement is technically right, but it doesn't answer the problem, on descent hp should be open(idle) and he receives an eicas msg that per fim means hpsov is not closed.
So if time permits i would run the eng on a remote stand, and start troubleshooting from the results i found(real hpsov failure or indic failure) or lock the vlv out per mel.
This snag is just as AP inop(no flightphase,mode, etc) and means nothing
So even before starting looking at muscle press lines, smooth vlv movement, etc, you might run at the stand on idle first and make an idea about this.
At least you know for sure wich vlv to properly lock out for mel(hpsov or prsov)