"Environment subfigure undefined" on journal submission
or you can try:
\usepackage{subcaption}
\captionsetup{compatibility=false}
I would suggest a work-around, if all else fails, as it is difficult to test this without going through the submission process yourself. In that regard, avoid using the subfigure
environment altogether, and default to using a tabular
structure for arranging your subfigures. While this comes with manual numbering of subfigures, it's not that difficult to maintain references manually.
Here's a minimal example that should show you the implementation:
\documentclass[smallextended]{svjour3}
\usepackage{lipsum}% Just for this example
\usepackage{graphicx}
\begin{document}
See Figure~\ref{fig:myfig}(a) or~(b). \lipsum[1]
\begin{figure}
\centering
\begin{tabular}{@{}c@{}}
\includegraphics[width=.7\linewidth,height=75pt]{example-image-a} \\[\abovecaptionskip]
\small (a) An image
\end{tabular}
\vspace{\floatsep}
\begin{tabular}{@{}c@{}}
\includegraphics[width=.6\linewidth,height=100pt]{example-image-b} \\[\abovecaptionskip]
\small (b) Another image
\end{tabular}
\caption{This is a figure caption}\label{fig:myfig}
\end{figure}
\lipsum[2]
\end{document}