From this question I used the following codes to add an empty INTENTIONALLY LEFT BLANK page if a section ended in an odd number of pages, as well as if the total document would end in an odd number of pages (because for some reason it doesn't add the blankpage to the last section)
\newcommand*{\blankpage}{%
%\setlength{\topskip}{0pt}%
% \setlength{\parskip}{0pt}%
\vspace*{\fill}
{ \centering INTENTIONALLY LEFT BLANK.\par}
\vspace{\fill}}
\makeatletter
\renewcommand*{\cleardoublepage}{\clearpage\if@twoside \ifodd\c@page\else
\blankpage
\newpage
\if@twocolumn\hbox{}\newpage\fi\fi\fi}
\makeatother
\AtEndDocument{%
\ifthenelse{\isodd{\pageref{LastPage}}}{\null\blankpage}{}}
Now here's my own question: the code made by the famous @DavidCarlisle seems to hint that if a two column setup is used, it would still place the "INTENT...BLANK" part right in the middle of the page. And it did! And then suddenly, it stopped doing it and started placing it on the left side of the page which I would guess to be centered in the left column. So how can I overrule the two columns and still have the sentence placed in the middle? The last page seems to be doing it right even though the \end{multicols} is after that last section.
{}on the gui. – Feb 06 '17 at 05:03