Read your bug report. Not sure it is a bug because footnote behaviour when page becomes full is not immediately obvious.
For better diagnostic, create a sample file from your original, making sure there is still the problem. As you state that contents is private, replace it with “lorem ipsum” (type lorem and immediately F3
Witer tries to keep a note and its anchor on the same page, flushing the anchor line to next page if needed. But this takes into account the widow/orphan policy in main text leading to superfluous-felt text move.
If note text is made of several paragraphs (or a long paragraph), then the note may be split with some contents rejected on next page.
I have practically never seen an anchor separated from its note. So please provide a sample.
Of course, all these rules are valid only if your document is saved .odt.
I’m using 7.4.2.3.