Cookies! Either you didn't allow them or deleted them later by cleaning something, using programs that clean data, changing security settings of your browser, having data removed by extensions to keep your browser clean and lean... the simplest thing removes what you think the website had had saved, and you start all over with settings. That's what cookies are there for too, to save settings. No cookies, no cigar.
Or haven't you ever thought about how or where websites save your personal data? You probably didn't click on something by mistake, you unintentionally removed data or intentionally but weren't aware of a rather global and not just local effect. Happens a lot with folks on PCs. I read this also a lot here, that people suddenly miss what they had just set and don't know why it works again but has changed in the first place and so on. That's the first thing that comes to my mind: cookies. Only essential cookies allowed, everything else rejected or none at all, deleted them later on with other programs or by using browser settings. It's that simple. Technology or machines do not make mistakes. Humans do.