Some classes (for example, book and report) set up a different set of footnotes per chapter, by resetting the footnote number at the start of the chapter. This is essentially the same action as that of equation, figure and table numbers, except that footnote numbers don't get “decorated” with the chapter number, as happens with those other numbers.
The solution is the same (requiring
the chngcntr package for LaTeX releases
prior to 2018); since the
numbers aren't “decorated” you can use the
variant; the code:
is all you need