I've had an issue on 2 completely different machines both using windows live mail 2011. First call I received I taught it was a user mistake. But when my neighbor came to me with the same problem after only 10 minutes after his upgrade and only using WLM11 I figured this might be on account of W10.
Both upgraded to windows 10 and their contacts dissappeared.
So I started my search and found numerous topics on where to find the contact lists.
Going to the directory I found a few folders that I all checked but showed empty as if they were gone.
I then checked the folder size of the complete "Contacts" folder. Which in one case was over 160 MB, and in the other over 188 MB.
This size was given to folders that show completely empty apart from the folders itself. So technically windows 10 shows me empty folders but shows a size of more than 160&180 MB.
Could it be that windows 10 hides files? I've also checked "hidden" files but nothing there either. Has w10 corrupted the data in these folders? Is there any way to recover his contacts? He & she never signed in with WLM11.