This seems to be a bug of inkscape. After the conversion of svg to pdf all pages above 25 seems to be missing in the ./svg-inkscape/uml_svg-tex.pdf_tex file. You can edit the file and add them like in the code below.
To not accidentally overwrite your file, you might want to change the name and include it with
\def\svgwidth{\textwidth}
\input{YourNewName.pdf_tex}
instead of \includesvg[width=\textwidth]{uml}
%% Creator: Inkscape inkscape 0.91, www.inkscape.org
%% PDF/EPS/PS + LaTeX output extension by Johan Engelen, 2010
%% Accompanies image file 'uml_svg-tex.pdf' (pdf, eps, ps)
%%
%% To include the image in your LaTeX document, write
%% \input{<filename>.pdf_tex}
%% instead of
%% \includegraphics{<filename>.pdf}
%% To scale the image, write
%% \def\svgwidth{<desired width>}
%% \input{<filename>.pdf_tex}
%% instead of
%% \includegraphics[width=<desired width>]{<filename>.pdf}
%%
%% Images with a different path to the parent latex file can
%% be accessed with the `import' package (which may need to be
%% installed) using
%% \usepackage{import}
%% in the preamble, and then including the image with
%% \import{<path to file>}{<filename>.pdf_tex}
%% Alternatively, one can specify
%% \graphicspath{{<path to file>/}}
%%
%% For more information, please see info/svg-inkscape on CTAN:
%% http://tug.ctan.org/tex-archive/info/svg-inkscape
%%
\begingroup%
\makeatletter%
\providecommand\color[2][]{%
\errmessage{(Inkscape) Color is used for the text in Inkscape, but the package 'color.sty' is not loaded}%
\renewcommand\color[2][]{}%
}%
\providecommand\transparent[1]{%
\errmessage{(Inkscape) Transparency is used (non-zero) for the text in Inkscape, but the package 'transparent.sty' is not loaded}%
\renewcommand\transparent[1]{}%
}%
\providecommand\rotatebox[2]{#2}%
\ifx\svgwidth\undefined%
\setlength{\unitlength}{592.8bp}%
\ifx\svgscale\undefined%
\relax%
\else%
\setlength{\unitlength}{\unitlength * \real{\svgscale}}%
\fi%
\else%
\setlength{\unitlength}{\svgwidth}%
\fi%
\global\let\svgwidth\undefined%
\global\let\svgscale\undefined%
\makeatother%
\begin{picture}(1,0.48717949)%
\put(0,0){\includegraphics[width=\unitlength,page=1]{uml_svg-tex.pdf}}%
\put(0.03036437,0.07219973){\makebox(0,0)[lb]{\smash{Maladie}}}%
\put(0,0){\includegraphics[width=\unitlength,page=2]{uml_svg-tex.pdf}}%
\put(0.2780027,0.07137733){\makebox(0,0)[lb]{\smash{Médicament}}}%
\put(0,0){\includegraphics[width=\unitlength,page=3]{uml_svg-tex.pdf}}%
\put(0.58164642,0.20633009){\makebox(0,0)[lb]{\smash{Matériel}}}%
\put(0,0){\includegraphics[width=\unitlength,page=4]{uml_svg-tex.pdf}}%
\put(0.84075574,0.20633009){\makebox(0,0)[lb]{\smash{Nourriture}}}%
\put(0,0){\includegraphics[width=\unitlength,page=5]{uml_svg-tex.pdf}}%
\put(0.57354926,0.07137733){\makebox(0,0)[lb]{\smash{\textit{Stockable}}}}%
\put(0,0){\includegraphics[width=\unitlength,page=6]{uml_svg-tex.pdf}}%
\put(0.82726046,0.34128286){\makebox(0,0)[lb]{\smash{Classification}}}%
\put(0,0){\includegraphics[width=\unitlength,page=7]{uml_svg-tex.pdf}}%
\put(0.31174089,0.46274035){\makebox(0,0)[lb]{\smash{Rang}}}%
\put(0,0){\includegraphics[width=\unitlength,page=8]{uml_svg-tex.pdf}}%
\put(0.28340081,0.20633009){\makebox(0,0)[lb]{\smash{\textit{Événement}}}}%
\put(0,0){\includegraphics[width=\unitlength,page=9]{uml_svg-tex.pdf}}%
\put(0.03103914,0.34128286){\makebox(0,0)[lb]{\smash{Contrat}}}%
\put(0,0){\includegraphics[width=\unitlength,page=10]{uml_svg-tex.pdf}}%
\put(0.58704453,0.34128286){\makebox(0,0)[lb]{\smash{Animal}}}%
\put(0,0){\includegraphics[width=\unitlength,page=11]{uml_svg-tex.pdf}}%
\put(0.2928475,0.34128286){\makebox(0,0)[lb]{\smash{Personne }}}%
\put(0,0){\includegraphics[width=\unitlength,page=12]{uml_svg-tex.pdf}}%
\put(0.39676113,0.11740891){\makebox(0,0)[lb]{\smash{n}}}%
\put(0,0){\includegraphics[width=\unitlength,page=13]{uml_svg-tex.pdf}}%
\put(0.98380567,0.31969042){\makebox(0,0)[lb]{\smash{1}}}%
\put(0,0){\includegraphics[width=\unitlength,page=14]{uml_svg-tex.pdf}}%
\put(0.07287449,0.11740891){\makebox(0,0)[lb]{\smash{n}}}%
\put(0,0){\includegraphics[width=\unitlength,page=15]{uml_svg-tex.pdf}}%
\put(0.28879892,0.11740891){\makebox(0,0)[lb]{\smash{n}}}%
\put(0,0){\includegraphics[width=\unitlength,page=16]{uml_svg-tex.pdf}}%
\put(0.23424845,0.04978489){\makebox(0,0)[lb]{\smash{n}}}%
\put(0.16059379,0.04978489){\makebox(0,0)[lb]{\smash{n}}}%
\put(0,0){\includegraphics[width=\unitlength,page=17]{uml_svg-tex.pdf}}%
\put(0.89608637,0.27245695){\makebox(0,0)[lb]{\smash{1}}}%
\put(0,0){\includegraphics[width=\unitlength,page=18]{uml_svg-tex.pdf}}%
\put(0.95006748,0.38731444){\makebox(0,0)[lb]{\smash{0..1}}}%
\put(0,0){\includegraphics[width=\unitlength,page=19]{uml_svg-tex.pdf}}%
\put(0.78801876,0.31969042){\makebox(0,0)[lb]{\smash{1}}}%
\put(0,0){\includegraphics[width=\unitlength,page=20]{uml_svg-tex.pdf}}%
\put(0.34278003,0.40740971){\makebox(0,0)[lb]{\smash{1}}}%
\put(0,0){\includegraphics[width=\unitlength,page=21]{uml_svg-tex.pdf}}%
\put(0.42802753,0.2214216){\makebox(0,0)[lb]{\smash{1..n}}}%
\put(0.49573064,0.28300648){\makebox(0,0)[lb]{\smash{0..1}}}%
\put(0,0){\includegraphics[width=\unitlength,page=22]{uml_svg-tex.pdf}}%
\put(0.34278003,0.25236167){\makebox(0,0)[lb]{\smash{1..n}}}%
\put(0.34278003,0.27245695){\makebox(0,0)[lb]{\smash{n}}}%
\put(0,0){\includegraphics[width=\unitlength,page=23]{uml_svg-tex.pdf}}%
\put(0.15770904,0.28228502){\makebox(0,0)[lb]{\smash{1}}}%
\put(0,0){\includegraphics[width=\unitlength,page=24]{uml_svg-tex.pdf}}%
\put(0.23471241,0.31969042){\makebox(0,0)[lb]{\smash{1}}}%
\put(0.16059379,0.31969042){\makebox(0,0)[lb]{\smash{0..1}}}%
\put(0,0){\includegraphics[width=\unitlength,page=25]{uml_svg-tex.pdf}}%
\put(0.43049933,0.31969042){\makebox(0,0)[lb]{\smash{1}}}%
\put(0.51764926,0.31969042){\makebox(0,0)[lb]{\smash{n}}}%
\put(0,0){\includegraphics[width=\unitlength,page=26]{uml_svg-tex.pdf}}%
\put(0,0){\includegraphics[width=\unitlength,page=27]{uml_svg-tex.pdf}}%
\put(0,0){\includegraphics[width=\unitlength,page=28]{uml_svg-tex.pdf}}%
\put(0,0){\includegraphics[width=\unitlength,page=29]{uml_svg-tex.pdf}}%
\put(0,0){\includegraphics[width=\unitlength,page=30]{uml_svg-tex.pdf}}%
\put(0,0){\includegraphics[width=\unitlength,page=31]{uml_svg-tex.pdf}}%
\end{picture}%
\endgroup%

alternatively you could do the conversion from .svg to .pdf yourself and prevent the creation of separate layers, see e.g. https://tex.stackexchange.com/a/350175/36296
width=\textwidthis no valid package option of the svg package. Do you mean\includesvg[width=\textwidth]{uml}? – samcarter_is_at_topanswers.xyz Dec 13 '18 at 15:00