Seems like it has issues on Firefox. 
Same for me, on Vivaldi. Cookies are allowed, though. It is some privacy setting I cannot find or disable, not sure what exactly.
It is sad that the Twine or Sugarcube authors ignore this problem, though it exists for years and people regularly report it on the Twine discord. I can access local storage fine, and other websites/games can do to, e.g. Paperclip AI. It should be possible for Twine to get it right, too.
John Ayliff, your game Seedship does work fine though. Is the difference that you do not use any save features there?
Sorry for the rant, it’s just so unnecessary and disappointing.
I don't know why this game would have the problem if Seedship doesn't. If you had cookies disabled and have just enabled them, try clearing your cache and reloading this page? Both games use the save features in the same way, and in any case I think this problem is to do with how Sugarcube stores the current game state, not the save system.
I agree, it would be nice if Sugarcube could at least show a "you need to enable cookies" message rather than an incomprehensible error.
You are correct, it is indeed cookies, especially 3rd party cookies. Not sure why Seedship worked in first place, but may be possible I played it on your website, not on itch.
So if anyone else is having this problem: Click the lock icon infront of the URL in the adress bar, go to “Cookies”, then select and allow the one containing “ssl.hwcdn.net” (that’s for vivaldi and probably works for other chrome-based browsers).
Thanks for the helpful hint and sorry again for ranting about SC on your games’ page! :D