Sometime yesterday, itchio moved all of their HTML games from one internal server to another internal server, which means the location the game was saving to no longer existed.
If you'd like to read more, you can here:
https://itch.io/t/3099694/notice-for-html-game-devs-upcoming-change-to-cdn-domai...
The issue is not something I can help you resolve. However if you come to the discord server, I can get you set up with an exe build of the game that has an approximation to the progress you made.
I figured there was some reason why the Discord link wasn't shared in plaintext on this page (maybe to protect against bots?), so I obscured it with rot13. rot13 = copy the string from my comment into the site rot13.com to convert it into the actual discord URL. I just checked and that does still work.