Book class: Abstract material fits on a left-hand (verso) page but not on a right-hand (recto) page

Question

I am finalizing my thesis, I wrote my abstract, and I compressed everything to fit nicely on one page. Now I realized that my abstract was on a left-hand page but it needs to be on a right-hand page, so I added a \cleardoublepage instruction.

However, after doing so my abstract does not fit on one page anymore. It now has a complete paragraph that spills over to the next page.

\documentclass[a4paper,12pt]{book}
\usepackage{pdfpages}
\usepackage{verbatim}
\usepackage{stmaryrd}
\usepackage{array}
\usepackage{vub}
\usepackage[T1]{fontenc}
\usepackage[scaled]{uarial}
\usepackage{tocloft}
\usepackage{blindtext}
\usepackage{fancyhdr}
\newcolumntype{C}[1]{>{\centering\let\newline\\\arraybackslash\hspace{0pt}}m{#1}}
\newcolumntype{L}[1]{>{\raggedright\let\newline\\\arraybackslash\hspace{0pt}}m{#1}}
\setlength{\marginparwidth}{0pt}
\makeatletter

\makeatother
\geometry{textwidth=390pt}

\geometry{bindingoffset=2cm}


\begin{document}
    \maketitle

    % I want a blank page in between title page and abstract
    % I tried the following two commands, both show the same issue
    \cleardoublepage
    \newpage\null\thispagestyle{empty}\newpage

    \cleardoublepage
    \setcounter{page}{1}
    \pagenumbering{roman}
    \input{sections/abstract}
    % ...

\end{document}

Even when i add a blank left-hand page with \newpage\null\thispagestyle{empty}\newpage instead of \cleardoublepage, the problem still persists. It seems like right-hand pages are less long than left-hand pages. Is this even possible?

And this is the vub package:

\ProvidesPackage{vub}
\RequirePackage{color}
\RequirePackage{ifxetex}
\RequirePackage{tikz}
\RequirePackage{adjustbox}
% VUB is in Belgium, we use A4
% Additionally, we use `geometry` to play with margins on the title page
\RequirePackage[a4paper]{geometry}
%\RequirePackage[T1]{fontenc}

\RequirePackage{kvoptions}
\DeclareBoolOption[false]{spotcolors}
\DeclareComplementaryOption{nospotcolors}{spotcolors}
\ProcessKeyvalOptions*{}

\ifvub@spotcolors
\RequirePackage[spotcolors]{vubprivate}
\else
\RequirePackage{vubprivate}
\fi

\newcommand\@faculty{Set a faculty using \textbackslash faculty\{\textit{Engineering Sciences}\}}
\newcommand\@subtitle{}

\newcommand\pretitle[1]{%
  \makeatletter%
  \newcommand\@pretitle{#1}%
  \makeatother%
}

\newcommand\promotors[1]{%
  \makeatletter%
  \newcommand\@promotors{#1}%
  \makeatother%
}

\@ifundefined{faculty}{%
    \newcommand{\faculty}[1]{%
        \makeatletter%
        \renewcommand\@faculty{#1}%
        \makeatother%
    }%
}

\@ifundefined{subtitle}{%
    \newcommand{\subtitle}[1]{%
        \makeatletter%
        \renewcommand\@subtitle{#1}%
        \makeatother%
    }%
}

\renewcommand\maketitle{
\begin{titlepage}
    \newgeometry{left=18mm,top=20mm,right=10mm}
    \begin{minipage}{\dimexpr\textwidth}
      \raisebox{\dimexpr \triangleH-\height\relax}{\includegraphics[width=5.66cm]{vub_logo_cmyk}}%
      \hfill%
      \vubtriangle
    \end{minipage}

    \vfill

    \hspace{25mm}\begin{minipage}{\dimexpr\textwidth-58mm}
        \ifdefined\@pretitle%
            \vubfont\small\color{vuboranje}\@pretitle
        \fi

        \vubfontbf{\color{vubbleu}\flushleft{\Huge\expandafter\uppercase\expandafter{\@title}}}

        \vspace{5mm}

        {\color{vubbleu} \LARGE\vubfont\@subtitle}

        \vspace{3cm}

        {\color{vuboranje} \large\vubfont\@author}

        \vspace{5mm}

        {\color{vubbleu} \large\vubfont\@date}
    \end{minipage}

    \vfill

%    \hspace{25mm}\begin{minipage}{\dimexpr\textwidth-58mm}
%        \ifdefined\@promotors%
%            \vubfont{\color{vubbleu}\@promotors}
%
%            \vspace{2mm}
%        \fi
%
%        \vubfontbf{\color{vubbleu}\fontsize{10pt}{10pt}\selectfont \@faculty}
%    \end{minipage}

    \hspace{25mm}\begin{minipage}{\dimexpr\textwidth-58mm}
        \ifdefined\@promotors%
                \vubfont{\color{vuboranje}Promotor:\\}
                %\vspace{1mm}
            \vubfont{\color{vubbleu}\@promotors}

            \vspace{2mm}
        \fi

        \vubfontbf{\color{vubbleu} \@faculty}
    \end{minipage}
    \restoregeometry
\end{titlepage}
}

\endinput

Thanks for your help!

EDIT: The abstract is structured as follows:

\section*{Abstract}
% ... large text that should fit one page ...

There are 6 lines that spill on to the next page.

To give you a visual clue of what's happening and why i think right-hand pages are less long, this is without a white page (so this is a left-hand page):

With a white page (this is a right page):

Notice that i left the phrase that is common to both versions.

Answer 1

Your problem is that you are changing the page geometry inside a group, the titlepage environment. This is wrong. Changing page geometry in the middle of a document is not easy and \newgeometry and \restoregeometry should be always used at the document level. When used inside a group it leads to inconsistent \textheight:

\documentclass{book}
\usepackage{geometry,lipsum}

\begin{document}
\begingroup
\newgeometry{left=18mm,top=20mm,right=10mm}
blub
\restoregeometry
\endgroup

\lipsum \lipsum \lipsum

\end{document}

If you correct the titlepage code the current abstract page will be shorter. So you will either have to shorten the abstract text or use \enlargethispage if you want to keep everything on one page.