For a good understanding, I have been using the GRM plugins for almost two decades.
The GRM tools are extremely old, and only have been (badly) re-packed every now and then.
They never worked properly, and, to be honest, I am surprised that they keep on working, knowing that they are still Vst2.
I admit that they have a few nice plugins for weird sound design, but the are such a PITA to use.
I use them only for offline processing.
That being said, have you tried the Nuendo doppler yet?
A thousand times better -and easier to use- than the GRM one
Fredo