I actually had my Hue lights listed 3 times and I finally figured out why.
I had a Hue hub, and Harmony Hub, and Alexa all connected to each other. This caused a very vicious circle. My set up looked something like this:
Hue <<>> Smartthing
Hue <<>> Harmony
Hue <<>> Alexa
Alexa <<>> Harmony
Alexa <<>> Smartthings
Note: if you have Hue and Harmony connected, you will pull in lights from Harmony as well (the dreaded 3rd device).
You really should only need to hook Hue to Smartthings and then Smartthing to Alexa. When you are done you should only have these connections:
Hue >> Smartthings
Harmony >> Smartthings
Alexa >> Smartthings
Basically you want your Smartthings hub to be the center of everything and then feed that out to Alexa.
If you connected everything to each other in a vicious circle like me, you would think that removing the Alexa skills for Hue and Harmony would solve the issue but it doesn’t. For some reason when you remove the Hue Skill from Alexa it doesn’t actually get removed.
TO FIX this you need to access your Hue control panel on a computer here:
Once here, delete all the connections from Hue to Alexa, and if you also allowed Harmony to connect to Hue you may want to delete that as well. If you actually use your Harmony remote to control your lights you could leave that connection but you may need to limit what Harmony shares with Smartthings using the process described above.
ALSO NOTE: I was also seeing this happen with my other devices like Wemo Switches. If I connect them to Both Smartthings and Alexa they were duplicated. Just something to keep in mind. Again, you want Smartthings to be the center of everything, and feed that to Alexa.
I sure hope this helps someone else. I know my OCD was really kicking in when I would see these duplicates in Alexa, as well as half the time I would get the device offline messages from Alexa but it would actually work.