I have noticed that you have to make sure when you make a "Command Request" you have to be 100% sure of the way things are set up and named. Other wise, "She" goes dumb. I can say "Turn Off xxxxxx" and it works most of the time. BUT I do run into the same problem you describe in many variations and sometimes it will work other times it won't.
What brand of lights or control system are you using? Mine is Lifx and I'm finding the integration of the Skill, of which I am finding Skills as a whole are severely lacking, and the Alexa App is the problem 98% of the time. To solve most of mine I have stripped things down to a bare minimum and unified so that "She" understands and I remember the last thing that worked. One instance is when I tell "Her" to "Pause DISH" the Hopper Pauses. This is what it states you say to interact. But when I say "Play DISH", "She" wants to play some band I have never heard of. AND only by accident when I had to yell at "Her" "Echo Stop" in trying to get her to stop playing the music she is picking to play, the Hopper also starts playing!! So . . . But then there are times that I get the "Dumb at the moment and even though I have done this many times before". Now I have to say "Pause Hopper", since part of the simplification I have had to do was to name the DVR a single word name, to pause and to play "Pause Hopper". For two reasons, first the "play" anything command seems to be connected to "Her" playing music from Amazon Music; second, the remote control for the Hopper does not have a "Stop", just play/pause which off the remote is the same toggle command depending on what mode the DVR is at. And since "She" only responds to "Play" as "She" wants, I have to "Pause" again to get it to "Play". THEN there's times I can be so severely bland and it works. "Echo Play" and it plays.
For my lighting I have many "Scenes" set up from 0% to 100% with color and what fixtures preset. Then I just tell "Her" to "Play 50%" or "Echo Lantern 30" and I get brightness, fixture and whatever the color is set for that "Scene". Without them, I can say "Make (I have a couple of different room designations set up to control only certain lights) Lights (which all the floor lights) 50%". Or "Dim Media Room to 60%", even though the room is at 30%, Dim and Brighten are the same word. The key is the percentage. Sometimes I feel it's "Her" job to make me numb.
I just got done going round and round with Samsung after they broke their "SmartThings" app with an update on January 31st. Now it's all pretty looking and works great with newer gear, but are obviously phasing older (2016) gear out. ALTHOUGH!! at CES 2016, Samsung Bigwigs touted that year as "THE" example of all the great IoT with their "SmartThings" was going to be. So through extreme experimentation I was able to get my TV back to being able to be in the "Routine" it was in before things started failing. It goes "Off" again in my "Goodnight" routine. What a nightmare. But that was the "Third Party Vendor", Samsung. So there's that getting in the way.
There are a ton of variables that change often. So you have to stay on your toes about what works and what did but doesn't now and how the "Skills" say you say the commands . . . "Good Luck!!"