[Ben Christie]" have a gradient ramp effect that has two handles attached to the 'gradient position' nulls via an expression. But when I parent the 2 gradient position nulls to the master mover, the gradient messes up. Is there a way to have the gradient position handles ignore the master mover position?"
When you parent the "gradient position" nulls to the "master mover" null, it changes their frame of reference. Instead of referring to position relative to the comp, they refer to position relative to their new parent.
Since the gradient itself is not parented to the master mover, it needs position data in the coordinate space of the comp, not the coordinate space of some other null.
Use an expression like this on the gradient start/end point to convert from layer space to comp space:
l = thisComp.layer("Gradient Position 1");