Over a decade ago this caused a quite bit of head scratching for me as to why in our C# application a certificate's thumbprint was not matching with that in our App.config file, even though the characters were seemingly identical.

Turns out Windows Certificate Manager had an "easter egg" that if you copied a certificate's thumbprint to your clipboard it included a zero width space with it.

Very, very subtle and actually very hard to spot without doing a debug or something.

There is a Stack Overflow of exactly this issue: https://stackoverflow.com/questions/11115511/how-to-find-cer...

At some point (Windows 10?) Microsoft "fixed" the Certificate Manager to stop doing this.