Subsubsection floating

Question

The images below and the code show how 50° subsubsection is not where I placed it. Any solution?

\section{Experimental results}
      In this section the temperature vs time plots are shown and commented as well as the 
        bidimensional thermal wave developed by the heat flux flux provided. It is reminded 
           that every experiment lasts for 300 s (5 min).
         \subsection{Unidirection carbon fiber plate}
       \subsubsection{\SI{40}{\celsius}}
       \begin{figure} [h!]
            \centering
        \includegraphics[scale=0.7]{Immagini/PLQ 200-01-399 40° C/50x}
            \caption{Temperature vs time (s) of the measurement point placed at 50mm from the 
           center of the plate along the x axis.}
            \end{figure}
             \begin{figure} [h!]
              \centering
              \includegraphics[scale=0.7]{Immagini/PLQ 200-01-399 40° C/78x}
                \caption{Temperature vs time (s) of the measurement point placed at 78mm from 
      the center of the plate along the x axis.}
     \end{figure}
        \begin{figure} [h!]
          \centering
            \includegraphics[scale=0.7]{Immagini/PLQ 200-01-399 40° C/107x}
                  \caption{Temperature vs time (s) of the measurement point placed at 107mm 
           from the center of the plate along the x axis.}
           \end{figure}
             \begin{figure} [h!]
            \centering
                \includegraphics[scale=0.7]{Immagini/PLQ 200-01-399 40° C/30y}
           \caption{Temperature vs time (s) of the measurement point placed at 30mm from the 
        center of the plate along the y axis.}
            \end{figure}
         \begin{figure} [h!]
            \centering
            \includegraphics[scale=0.75]{Immagini/PLQ 200-01-399 40° C/export/queste/init}
            \caption{Thermal wave at t=5 s.}
          \end{figure}
          \begin{figure} [h!]
        \centering
        \includegraphics[scale=0.75]{Immagini/PLQ 200-01-399 40° C/export/queste/meta}
           \caption{Thermal wave at t=150 s.}
          \end{figure}
            \begin{figure} [h!]
              \centering
               \includegraphics[scale=0.75]{Immagini/PLQ 200-01-399 40° C/export/queste/fine}
             \caption{Thermal wave at t=300 s.}
             \end{figure}
               \subsubsection{\SI{50}{\celsius}}
             \begin{figure} [h!]
                \centering
                \includegraphics[scale=0.7]{Immagini/PLQ 200-01-399 50° C/50x}
                 \caption{Temperature vs time (s) of the measurement point placed at 50mm from 
             the center of the plate along the x axis.}
            \end{figure}
            \begin{figure} [h!]
          \centering
             \includegraphics[scale=0.7]{Immagini/PLQ 200-01-399 50° C/78x}
              \caption{Temperature vs time (s) of the measurement point placed at 78mm from 
       the center of the plate along the x axis.}
        \end{figure}
       \begin{figure} [h!]
            \centering
            \includegraphics[scale=0.7]{Immagini/PLQ 200-01-399 50° C/107x}
            \caption{Temperature vs time (s) of the measurement point placed at 107mm from the 
            center of the plate along the x axis.}
            \end{figure}
            \begin{figure} [h!]
                \centering
                \includegraphics[scale=0.7]{Immagini/PLQ 200-01-399 50° C/30y}
                   \caption{Temperature vs time (s) of the measurement point placed at 30mm 
                     from the center of the plate along the y axis.}
                 \end{figure}
                \begin{figure} [h!]
            \centering
                \includegraphics[scale=0.75]{Immagini/PLQ 200-01-399 50° C/export/queste/init}
            \caption{Thermal wave at t=5 s.}
                     \end{figure}
                         \begin{figure} [h!]
                            \centering
                        \includegraphics[scale=0.75]{Immagini/PLQ 200-01-399 50° 
                          C/export/queste/meta}
                           \caption{Thermal wave at t=150 s.}
                            \end{figure}
                       \begin{figure} [h!]
                            \centering
                        \includegraphics[scale=0.75]{Immagini/PLQ 200-01-399 50° 
                          C/export/queste/fine}
                                     \caption{Thermal wave at t=300 s.}
                             \end{figure}