Hi,
weight derivatives are not parallelized. A solution would be to run the geometry optimization in parallel without weight derivatives, then turn to serial mode and add weight derivatives. A subsequent geometry optimization should do very few cycles as I expect the corrections from the weight derivatives to be quite small. The final NumForce should be run with the serial binaries and with the -mfile option anyway, this is much more efficient than using the parallel binaries.
Regards,
Uwe