There is an intermittent issue with the recently-released Lionel 2-6-0s derailing on curves. Lionel has investigated this issue, and found that it's caused by incorrectly-sized traction tires; when these engines were produced, the factory put on traction tires that are too thick.

If you're running into the problem, you can contact Lionel via TalkToUs@Lionel.com or 800-454-6635, and they'll send you replacement tires of the correct size.