[ownedbycats]

https://github.com/JimmXinu/FanFicFa...g-errors--help

Browser caches can sometimes become (mildly) corrupted and/or FFF's cache reading code is less than perfect. I suspect the answer is probably both.

Your best bet in such a case is to clear your browser cache before trying again with all steps, including visiting the pages in browser.

If that doesn't help, some users have reported success manually deleting the contents of their browser cache directory; then the browser should recreate it entirely. I'd quit the browser and back up first before trying again.