you have to get escalated to the kindle support debt to see any non amazon devices attached to your account. can NOT been seen in your dashboard by you OR amazon support!!!
You had 1 job amazon!!!
EDIT: check out these tweets from samsung that samsung later deleted about A/V on their TVs needing updated, https://www.reddit.com/r/sysadmin/comments/dpbt3t/the_perils_of_security_and_how_i_finally_resolved/f5vgpye/
EDIT: amazon unlike netflix or even yahoo has no force sign out all devices
Last I checked, you can’t with google and chrome. I think gmail does, but not chrome.
I just deleted a bunch of my old phones from my account, no problem there. Go to your account page and under Digital content and devices click Content and Devices, then switch from the Content tab to the Devices tab.
That is how it works on Amazon.de
Just did the same. And put in a new password.
In case it won’t let you remove a device with an Amazon Shopping app, you can try and delete the “voice recordings”. Had that happen and after I clicked on “Delete voice recordings” I was able to remove the device.
Oh. I did that anyway but good to know for everyone else. 
Could be an inside job: