Long text in multirow

A solution could be to use the \Gape command (from the makecell package) to increase the height of the cells in the second column that correspond to the \multirow in the first column. The value of the optional argument has to be determined experimentally, as it depends on the font/ fontsize. You also have to put the long text in a \parbox inside multirow.

Another solution, also with makecell consists in making both cells in the second column \multirowcells, of the (same) relevant number of rows, and the long text a \multirowcell of twice this number of rows.

Both solutions are illustrated in the following code:

\documentclass[a4paper,12pt]{report}
\usepackage[utf8]{inputenc}
\usepackage{fourier}

\usepackage{multirow}
\usepackage{longtable}

\usepackage{makecell}

\begin{document}

\begin{longtable}{|m{\dimexpr0.5\linewidth-2\tabcolsep\relax}|m{\dimexpr0.5\linewidth-2\tabcolsep\relax}|}
\caption{Title}
\tabularnewline\hline%
\multirow{2}{*}{\parbox{\linewidth}%
{\centering \scriptsize \textbf{Long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long}}}
& \Gape[12pt]{\scriptsize 11} \tabularnewline
\cline{2-2}
& \Gape[12pt]{\scriptsize 11} \tabularnewline
 \cline{1-2}
\end{longtable}\bigskip

{\normalsize
\begin{longtable}{|m{\dimexpr0.5\linewidth-2\tabcolsep\relax}|m{\dimexpr0.5\linewidth-2\tabcolsep\relax}|}
\caption{Title}
\tabularnewline\hline%
\multirowcell{8}{\parbox{\linewidth}
{\centering \textbf{Long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long}}}
&\multirowcell{4}{11} \tabularnewline & \tabularnewline & \tabularnewline & \tabularnewline
\cline{2-2}
& \multirowcell{4}{11} \tabularnewline & \tabularnewline & \tabularnewline & \tabularnewline
 \cline{1-2}
\end{longtable}
}
\end{document}