If anyones been facing issue with page password protection, I may have found a temporary solution.
Issue: Page level (even folder level) passwords were coming as incorrect (in publish and preview). I tried various different passwords and copied and pasted but I was constantly getting the incorrect password error message.
Potential solution/hack: Try setting a site level password, enable it, see if its working after publishing and then disable it. Now set a new page level password again and it should work.
Let me know if this helps anyone or helps uncover some bugs.