I have just recently had the same problem.  All but 3 of my steamer would derail on Atlas turnouts.  After further investigation I notice that they were only derailing on a few of the Atlas turnouts.  So I pulled one that was causing details and one that was working.  And did a comparison and too my surprise there were diffrent.   

first the working turnout had stamped points.  The problem one had cast points.

second the frog spacing and amount of plastic was diffrent. 

So I emailed Atlas and yes they did change the code 80 turnouts.  And you guesses it,  The new ones are the cast point type. 

the problem with the new turnouts are that the cast points are not as thin and the stamped steal.  And the frog spacing is to tight for models with wide flanges. AKA Model Power steams and most Bachmann steam but the 2-8-0 Spec.  It looks your locomotive is going over a speed bump on one side when it pass over one of the new turnouts.

So look at your switch and see if you have stamped points or cast points.