Well, if everything else is fine on it, then they are all wrong and the switch is wrong, or just your FA is having problems.
(I think the answer is clear, but you can improve Aristo switches, see my site)
First check the gauge of all the wheels (compare them to your other locos) I'll bet is is not it.
Next check that the loco trucks swivel nicely and freely, grease if needed. This is possible, might be he problem.
Last, check that your brand new FA, that is much lower than the previous models, is not hitting the track with the pilot as it goes through the switch. This means the switch is level, and the track connecting to it is level and smooth. Check the cross level of the tracks too.
"Grounding" of the pilot on the unlevel track is very common with this loco.
I think this is your problem, if I have to guess with very little information.
Thanks Greg. I have already raised the pilot and made sure the trucks are free moving. I will check the wheel gauge. The engine is more sensitive to track conditions than my other engines. When it goes the switches I can some times hear a "bump" near the frog and other times not.
I will let you know how the gauge is.