I am using fancydhr for my title page to display logos on its header and footer. For the rest of my report I use \pagestyle{plain} to get the standard footer with only the page number. But using the \pagestyle{fancy} on the first page causes the entire document to be like shifted down, and the page numbering disappears. I can only recover it by increasing the bottom margin up to 6 cm but it keeps a 6 cm space between the end of the text and the end of the page, so this solution does not suit me well.
Here is my code with my desired margins :
\documentclass[11pt,a4paper]{report}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage[french]{babel}
\usepackage{ragged2e}
\usepackage{graphicx}
\usepackage{esint}
\usepackage{gensymb}
\usepackage{lipsum}
\usepackage{fancyhdr}
\usepackage[left=2.5cm, right=2.5cm, top=2cm, bottom=2cm, includehead, includefoot, heightrounded, footskip=30pt, headheight=12pt]{geometry}
\usepackage{titlesec}
\usepackage[pdfa]{hyperref}
\setlength{\parindent}{4ex} % alinea size
\hypersetup{linkbordercolor=1 1 1, urlbordercolor=1 1 1}
% ============================ Header with logo ===============================
% -----------------------------------
\renewcommand{\headrulewidth}{0pt} % supprime la ligne de header
\fancyhf{}
% ------------- Header --------------
\fancyhead[L]{\includegraphics[width=2.5cm]{example-image-a}}
\fancyhead[R]{\includegraphics[width=2.5cm]{example-image-b}}
\fancyhead[C]{\includegraphics[width=2.5cm]{example-image-c}}
% ------------- Footer --------------
\fancyfoot[L]{\includegraphics[width=4.5cm]{example-image-b}}
\fancyfoot[R]{\includegraphics[width=4.5cm]{example-image-b}}
% -----------------------------------
\pagestyle{plain}
% ==============================================================================
% ================================= DOCUMENT ===================================
% ==============================================================================
\begin{document}
% Title Page
\thispagestyle{fancy}
\vspace*{3cm}
\begin{center}
\Huge \textsc{Rapport de stage}\\
\vspace{10mm}
\large \textit{présenté par}\\
\vspace{5mm}
\Large \textbf{Anderson DA SILVA} \\
\vspace{7mm}
\hrulefill \\
\vspace{0,5cm}
\Huge \textbf{Étude de la couche limite atmosphérique en Atlantique tropical dans le cadre de la campagne EUREC$^4$A}\\
\hrulefill \\
\vspace{10mm}
\large Stage effectué au LATMOS du \textit{19 avril 2021} au \textit{19 juillet 2021}.\\
Sous la direction et la tutelle de \textbf{Richard WILSON} et de \textbf{Hugo BELLENGER}.\\ \vspace{1cm}
\newpage
\end{center}
% -------------- Document corps ----------------
\lipsum[1-24]
\end{document}