I have the same problem.
I activated some devices on my Adobe ID but I can't remember which among the many computers/laptops/ereader that I use.
Probably one of the activated devices is even an old pc which is broken! But I have no way to discover this. At least, I couldn't find it.
So I subscribe the opening question: can anyone tell how to check which devices are activated on my ID?
Ideally, it would be nice to have a "Registered Devices" tab in your adobe account at Adobe ID where you can see which devices are registered with your account and where you can manage (at least, delete) them.
This are not possible. You can check only the Authorize in your Program or your Reader.