Are you using the same user to unlock the page, that had actually locked the same page? If not, then you would need the actual user who had locked the page, or OOTB superuser named "admin" to unlock that page.
I created a user named "testUser" and added it to Administrators group:
1) I unlocked /content/we-retail/us/en page.
2) Then, I locked it back using the same testUser.