I am having similar issues with validating a W10 install. I looked on my devices listed on the Microsoft account page, and saw a whole stack of devices that I have no idea what they are?
Is a device added every time an install is done? How does this affect the product key being used? I have about 6 listed just as 'PC'.
Looks like every build of the Insider Preview W10 is listed!
What does 'remove device' actually do? Does it affect the key? Further validation? Is it best to remove everything except for the current legitimate devices?