Microsoft’s rolled out its anniversary update for Windows 10, and along with taking a long-ass time to install, it also introduced a problem on both my computers, so there’s a fairly good chance you might come across it too.
When trying to log in after the update, I found that the PIN I entered was deemed incorrect, even though I knew it definitely wasn’t. Same situation on both a laptop and desktop.
Logging in using a password worked just fine, but navigating to Settings > Users > PIN > Change didn’t, because, well, it thought I didn’t know the PIN.
What you can do, however, is just delete the existing PIN and re-set it. That should see you right again. Of course, if you don’t know your password, you’re going to have to jump few a few hoops to retrieve that too.