We are in the process of converting to Lighting Experience.  One issue we've ran into is tied to Price Books.  When users add products to opportunities in classic, they are defaulted to the appropriate Price Book.  When they add products to opportunities in LE, they are given a choice for which Price Book to choose.  I don't think it's a Price Book sharing issue as they don't have access to the "other" Price Books.  Has anyone else run into this issue?