There are really only two reasons why the the PUK would be blocked:
(1) If you entered the PUK wrong three times, either with yubico-piv-tool or the YubiKey PIV Manager
(2) If you initialized the PIV applet with the YubiKey PIV Manager and left the default setting of "Use PIN as key." This blocks the PUK. The reason for this is discussed here -
https://developers.yubico.com/yubikey-p ... t_Key.html (and you can always set a custom Management Key instead, which allows you to set a custom PUK as well)