I've recently bought a second hand motherboard. I installed windows 10 on it and activated it with my key.
However I've noticed that sometimes my background wallpaper changes into an image that isn't located on my pc.
I've checked the product code in powershell, using wmic path softwarelicensingservice get OA3xOriginalProductKey, and it shows a complete different code than I have installed in windows.
And yet when I check with slmgr /dli it does show my windows code.
What a strange problem. Thankfully you figured it out as far as you can.
I always prefer to use local account with windows.
I'm not a big fan of the way Microsoft lock the os to the hardware, but you don't hear of too many problems when people need to change things so I guess they have it about right.
I tested the pc at work (I build that one myself) with the powershell lines 'wmic path softwarelicensingservice get OA3xOriginalProductKey' and 'slmgr /dli'
And get this result.