The books use non-standard classnames for the footnotes. In these cases you need to view the HTML of the footnotes and manually add a book-specific style-tweak (last menu item) to give KOReader a hint.
In the first book (Upadek...), that book-specific style tweak is:
p.bodyfootnote { -cr-hint: footnote-inpage; }
On the second book, it's:
div.endnote { -cr-hint: footnote-inpage; }
More information here:
https://github.com/koreader/koreader...ent-1913228054