Password protect only works when logged in

I’ve been looking to make some updates to my base theme but it seems there’s an issue with the password protection functionality that I’m missing.

It works as expected when you’re logged into wp-admin and pages show the protected content but when you’re not logged into wp-admin and you try to view password protected pages/posts, entering the password simply loops back to the page with the protected message but removes the password field.

I’m guessing I’m missing some standard functionality in my theme somewhere but I can’t figure out what. Any pointers much appreciated.