Why is \newpage ignored sometimes ?

Floating figures and tables can move past \newpage, so what is happening is that the \newpage does start a new page, then inserts the figure, then starts the references section.

You want \clearpage, which has the same effect as \newpage but restricts floats as well. If there are pending floats when \clearpage hits, a float page is created only after which the content will continue.

For me works properly something like this, I force the creation of a new page with the invisible sign.

\clearpage
\newpage
\mbox{~}
\clearpage
\newpage