OnCropGather doesn't exist as of a few months ago, and has never existed with GrowableEntity (only as PlantEntity). You'll need to change to either OnGrowableGathered or OnGrowableGather.

void OnGrowableGathered(GrowableEntity growable, Item item, BasePlayer player)​

object OnGrowableGather(GrowableEntity growable, BasePlayer player)​