It may be that the moving switch blades are adding tension to that which the spring applies to the armature. I don't think Gottlieb specified the wrong springs, of course, they may have been substituted sometime in the past. It is always worth spending a bit of time making sure the moving switch blades exert minmum pressure on the ladder so they do not add excess pressure.
The image shapeshifter posted showed the armature had gone past being a full mating to the coil slug end, and wasn't sitting on it fully. I suspect the new, larger coil cured that problem by making the fit better. A slight modification of that armature could well have cured the problem as well.