When you use a mograph python effector switched to "full control" mode by default it doesn't work because of the absence of a falloff field. It took me awhile to figure out why my custom effectors didn't work coming from R18 to R20.
I would suggested updating the boilerplate in the effector when switching to full control mode to check for a falloff if that's possible. If not maybe fall back to commented out version for with falloff and without?