I have a Node.js/Express webapp deployed on a VPS using Dokku with two containers, one frontend, one backend. Recently got an https licence acquired for it and so I reconfigured both the frontend and backend to work with it, including the cookies. That was two days ago and it worked just fine all day in production. By yesterday, however, it would refuse to grant cookies on login, no matter the user and the number of tries. Since I deliberately wrote the code to automatically login anyone without cookies, this is a pretty big problem now. It's especially baffling how it could break from one day to another when literally nothing was done to it. It still works perfectly on my machine with localhost.
What could have happened to the cookies and how can I fix it?