Multiline subfigure caption cannot be shown fully

Question

It's covered by the picture form the next line as shown below:

I've tried to set subfigure with new width or new height, but the problem is still there.

The environment of my latex is a template on overleaf, I made a simple version and uploaded in Github here.

A simple version of the source code is as below:

\documentclass[type=master,fontset=fandol]{thuthesis}

\usepackage{thuthesis}

\graphicspath{{figures/}}


\begin{document}
\mainmatter

\chapter{test}

\begin{figure}[h]
  \centering%
  \begin{subfigure}{0.5\textwidth}
    \centering
    \includegraphics[width=\linewidth]{1.eps}
    \caption{$v_l^* - l$}
  \end{subfigure}%
%  \hspace{4em}%
  \begin{subfigure}{0.5\textwidth}
    \centering
    \includegraphics[width=\linewidth]{2.eps}
    \caption{$\sigma_l^* - l$}
  \end{subfigure}

  \begin{subfigure}{0.5\textwidth}
    \centering
    \includegraphics[width=\linewidth]{3.eps}
    \caption{$v_b - l$}
  \end{subfigure}%
%  \hspace{4em}%
  \begin{subfigure}{0.5\textwidth}
    \centering
    \includegraphics[width=\linewidth]{4.eps}
    \caption{$\sigma_b - l$}
  \end{subfigure}

  \caption{}
  \label{fig:ov}
\end{figure}

\end{document}

Answer 1

with your MWE, after small tweak of images width (from width=0.5\textwidth to 0.48\textwidth) and fixing error in document class (undefined\bibfont`), i obtain the following result:

Corrected MWE is:

\documentclass[type=master,fontset=fandol, demo]{thuthesis}
\usepackage{thuthesis}
%\graphicspath{{figures/}}
\usepackage{subcaption}

\begin{document}
\mainmatter

\chapter{test}
\begin{figure}[ht]
  \begin{subfigure}{0.48\textwidth}
    \includegraphics[width=\linewidth]{1}
    \caption{$v_l^* - l$}
  \end{subfigure}%
\hfill
  \begin{subfigure}{0.48\textwidth}
    \includegraphics[width=\linewidth]{2}
    \caption{$\sigma_l^* - l$}
  \end{subfigure}

  \begin{subfigure}{0.48\textwidth}
    \includegraphics[width=\linewidth]{3}
    \caption{$v_b - l$}
  \end{subfigure}%
\hfill
  \begin{subfigure}{0.48\textwidth}
    \includegraphics[width=\linewidth]{4}
    \caption{$\sigma_b - l$}
  \end{subfigure}

  \caption{}
  \label{fig:ov}
\end{figure}
\end{document}

• you not need to write image file tip (as you can see in MWE above)
• you should write to document class author and ask him to fix error: \bibfont undefined (temporally i change line 1149 from \renewcommand\bibfont{\ifthu@bachelor\wuhao[1.619]\else\wuhao[1.5]\fi} to \newcommand\bibfont{\ifthu@bachelor\wuhao[1.619]\else\wuhao[1.5]\fi}
• as you can see, images appear as expected, without any overlapping of sub-captions. if you like to have more space between sub-captions and images in the next row, insert \medskip or \bigskip before second rows of images:

... (images in the first row)
\end{subfigure}

\medskip
\begin{subfigure}{0.48\textwidth}
... (images in the second row)