Page password defaulting to old one - unable to change

Looking for some help updating my page password.

When I click on the page settings and select password protected I am not able to update my password from an old one.

I am able to clear the input and type in a new password I press 'save' settings close, but when I return to settings it has changed it to an old password. I have also tried it in multiple browsers but has not resolved the issue. 

Any advice would be really appreciated!