So I started the fight, got to phase three, threw in the towel. (It caught me off guard without my mouse pad, early in the morning, and I panicked!) Figured I'd try again later. It sent me back to the load screen after I died, and when I loaded, it had picked some WAY older save. Literally after I had finished my first Heart. All my progress is just gone. 
Playing the demo on itch.io

Urgh we can't replicate that bug or figure out the reason for it for the life of us. Happens on both Itch.io and on Steam.

Sneaky bugs are never fun, but Dark Forest is! If this info helps any later down the line, I'm using Brave, I did have uBlock on, but it only blocked itch.io's side-ad. If a site data dump would somehow help, let me know. I'll zip it up and drop it in a google drive link. ty for a wonderful game; that ending was a fun surprise!