Thanks for your reply, but I'm not sure if you have not quite seen the problem.
Try this.
1. Insert a footnote, type in the footnote using all the defaults (Helvetica Neue Regular 12 pt, or whatever your default is, it does not matter), make one word in italics or bold or underlined. Click the body of the document, to return to typing the body of the document.
2. Click the footnote to select it, you see that the footnote font is correctly shown (Helvetica Neue Regular, 12pt), and the font style is shown as "multiple" which is correct.
3. Click the body of the document, to return to typing the body of the document.
Insert a second footnote, writing the content of the footnote with different font size (any font size will suffice).
4. Click a footnote to select all footnotes.
The footnote font is correctly shown (Helvetica Neue Regular) and footnote font size is shown in grey italics, which indicates that there is more than one font size. You can then make all the footnotes the same font size by changing this number and hittig "return" - this is a very convenient feature for standardising footnotes.
Make both footnotes the same font size (this is not essential for the example I am explaining, but will make the remainder of the explanation easier to follow).
5. Click the body of the document, to return to typing the body of the document.
Insert a third footnote, writing the content of the footnote with different font (Times New Roman, 12pt, for example but any font will suffice).
6. Click a footnote to select all footnotes.
Footnote font is correctly shown (multiple, 12pt).
7. Change all the footnotes so that they are all in the same font (for example, double click the third footnote to select all of it, and then change the font; or click one footnote to select them all, and change the font).
8. Click the body of the document, to return to typing the body of the document.
Click a footnote to select all footnotes.
Footnote font is shown as multiple which is incorrect.
9. Click a footnote to select all footnotes.
Click italics to make all text in the footnotes italic.
Click the body of the document, to return to typing the body of the document.
Click a footnote to select all footnotes.
The footnote font is correctly shown (Helvetica Neue Regular).
10. Change one word in the footnotes to italics (or bold or underlined....)
Click a footnote to select all footnotes.
Footnote font is shown as multiple which is incorrect.
Conclusion: Pages appears to display incorrect information about the footnote fonts.
The only workaround is to never use any font style (italics, bold, underlining etc) in footnotes, but this appears to be a workaround for a fault in Pages.
Note: updated to Pages 13.0, same problem.
Thanks for taking the time to read this long reply.