My archived files in Windows Live Mail 2012 have disappeared

Years ago I set up an "Archived Items" folder in my Live Mail 2012 program and put important emails into it.  I was running Windows 7.  I recently upgraded the operating system to Windows 10 and don't care for the email program that comes with it, so I continue to use Live Mail.  I just noticed that when I open my Archived Items folder I see a listing of all of the items that have always been there, but when I click on any of them, the message in the pane says "Message Not Found".  The only message in the folder that I can still open up is the one that I archived after installing Windows 10.  I went into my files directory and found the Live Mail folders, but the one labeled "Archived Items" only has one file (the one I can still open in the mail program).  Why would all of the contents of my archived emails disappear?  Do you think there's a way to still retrieve them?