Unfortunately, this is a known issue when playing through the browser. Something I’ve not yet been able to isolate the cause of. Could you provide me with a few additional details?

1. Which browser do you use?
2. Are you using it on a laptop/desktop, rather than a mobile device?
3. Could you describe exactly when the error occurred: which battle, was it during the battle, was it during card exchange, etc

same here, after every battle. I hoped refreshing would allow me to hit continue game and move past it, but it doesn't autosave between the end of the battle and that point apparently. so sad , this looks real neat!!

playing in browser 

Chrome Version 139.0.7258.155 (Official Build) (arm64)

macos (laptop, not mobile)

same error as others: it crashes immediately after I pick my victory card at the first real battle after the tutorial. (I picked the first area on the list)

to be clear, it's certainly a neat project!