Blame yourself! Your file has two management flaws.
First, it is formatted exclusivement with direct formatting: everything (except notes because they are internally managed by Writer) is Default Paragraph Style with “decoration” manually added. Already, this will prevent you from formatting easily your document.
Second, the underlying XML is completely botched by some add-on you used for your citations. You mentioned Mendeley. As every “universal” add-on, Mendeley was built with M$ Word text managing philosophy and this behaviour was emulated when ported to LO Writer, breaking the built-in mechanisms.
In particular, it interacts for an unknown reason (for me) with footnotes. The Footnote paragraph style receives some weird and harmful text flow direct formatting requesting a page break before the note. This addition is so strange that it can’t be cleared manually.
This page break which seems to trigger in undefined circumstances is the cause of your problem.
I think Mendeley is messing up the document structure (for example there are non-displayed citations to ocean pollution with N2O and El Niño oscillation, unless you forgot to remove it from the database). You perhaps entered the notes in a Mendeley citation and it took over everything, by-passing the standard note mechanism.
Writer comes with a built-in bibliography feature which is perfectly integrated. But you must first learn how to configure and use it. I know, you must take the time for it. But you also need to learn how to work with styles.
Why did you choose to work with Mendeley? Which features did it offer that aren’t implemented in Writer? Do you really need them? Think about these questions and decide by yourself.
I highly recommend you read the Writer Guide. It contains a good introduction to styles. The description of the bibliography feature is a bit concise, so you have to discover it by practice.
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