Lock Screen Keyboard
Try going to Settings, then Password. Enter your lock screen password. Swipe down there are radio buttons under a heading that reads Allow access when locked. The last one is Reply with message. Try turning that one off.

If problem persists and you want an annoying non(long-term)solution, you can swipe right directly on the lock screen text to get a reply square. Selecting this will allow you to close out of the lock screen text and give you full access to the password entry screen so that you don't have to restart your phone.