While lo mein and chow mein do have similar characteristics and ingredients, they do have their differences. It is these differences that do cause both dishes to taste slightly different. While there is not a huge difference in the taste, it is noticeable.
The main difference in the taste of chow mein and lo mein is how they are cooked. When making lo mein, the noodles are tossed in the sauce and mixed in with the ingredients and not fried.
With chow mein, the noodles are fried, which causes them to be more crunchy in their texture and less soft in comparison to lo mein, even though both recipes use egg noodles.