Those little login headaches pop up more than they should. I ran into the exact same expired session thing a couple weeks back after switching devices – browser was holding onto old cookies or something. What fixed it for me was going incognito mode first to bypass cached data, then just entering credentials fresh. Also had an issue once where auto-fill added an extra space at the end of the password, super annoying. Now I always double-check the URL starts properly and avoid saved passwords if I'm on public Wi-Fi. Their main entry point makes it straightforward once you skip the redirects:
https://space-slots.com/ . Clean login flow there, no extra steps. Since sorting that out my access has been smooth every time, even on mobile during travel.