@handkgregory I can help answer this.
I had the same issue a few months back… Figured out that my 2nd unit hadn’t linked correctly and was given the same name as my 1st. I had to go into my Alexa App and remove it from the ‘Devices’ tab. Linking it back on the Dyson app 2nd time around solved it.
The ‘Devices’ tab shows the names the machines has been given. I suspect this correlates to the location chose when setting the machine up. In my case I have one in the Bedroom and the other in my Lounge.
Depending the machine, I can say either “Alexa, set the bedroom/lounge fan speed to x”
Try reviewing some article in the Knowledge Base.
https://community.dyson.com/amazon-alexa-56/controlling-your-machine-with-alexa-30More specifically ^^
Charlie.