I don't want to get too OT here, but just for the sake of information our own Lexa works fine in most cases except for the kitchen Dot (we have two Dots and Echo). There I have commands that turn on the Kitchen lights, and turn on the Kitchen TV. I can say "Lexa turn on Kitchen TV" or "Lexa turn on Kitchen" and it works fine. But when I say "Lexa turn off Kitchen TV" she will *sometimes* turn off both the TV as well as the kitchen lights.
The Kitchen TV is a Harmony command so it's not anywhere near the rest of the lights in the Kitchen group. And in either case she DOES execute the Harmony command -- it's just that sometimes she also turns off all the lights in the kitchen (three separate devices under one group). I thought for a bit it was the way I phrased it, so I tried "Lexa turn Kitchen TV off" and that seemed to work... until it didn't.
It's almost like there is a buffer where the word "Kitchen" gets stored and after she has resolved the full phrase "Kitchen TV" she then goes on to see if there is anything else that might match. In any case, my own advice is to name things VERY distinctly (like the other poster here, I would recommend NOT using the word "lights" in your groups) and then pray.