I'm not sure why that is failing. I tried a very similar expression with my example, using IC615 ISR17 and MMSIM131 ISR2 (so one later than you):
ipnVRI((v("/outp" ?result "pac") - v("/outm" ?result "pac")) '-2 '0 ?rport resultParam("load:r" ?result "pac") ?epoint -35 ?measure "Output")
And it worked fine in Monte Carlo...
Maybe it was a bug in that ISR - I don't have so easy access to that specific ISR at the moment since I'm at home for the Christmas break. Seems a bit unlikely though, but I know there have been some issues with the result separation stuff for monte carlo, so maybe that's it?
Can you check in the CIW:
to see what they return? I'm expecting all three to return "t".