CAS bundle (an Elsevier document class) - pdfTeX error (font expansion): auto expansion is only possible with scalable fonts

Question

I'm writing a scientific article using CAS bundle from Elsevier, which is a double-column format.

This how my document looks.

\documentclass[a4paper,fleqn]{cas-dc}
\usepackage[numbers]{natbib}
\usepackage{microtype}
\usepackage{amsmath,amssymb,amsthm,bm}
\usepackage{graphicx}
\usepackage[colorlinks]{hyperref}
\usepackage{url}
\usepackage{subcaption}
\usepackage{notoccite} 
\usepackage{float}
\usepackage{stfloats}
\usepackage{caption}

\begin{document}
\section{chapter1}
   ........  my text
\section{chapter2}
   ........  my text
\begin{figure}
   \centering
   \includegraphics[width=\linewidth]{fig1.jpg}
   \label{fig1}
   \caption{This is my problem area, can't have long text}
\end{figure}
   ........ my text
\end{document}

The issue that I'm facing is a little strange because when the caption length of the figure exceeds one line, it throws me this pdfTeX error (font expansion): auto expansion is only possible with scalable fonts.

However, I found that removing the microtype package allows me to have a long caption without any errors but the alignment in the rest of the document gets messed up. Based on the answers from previous posts related to this error, I tried to use \usepackage[T1]{fontenc}, \usepackage{lmodern}, and several options in microtype package (like protrusion, expansion, and final). None of these helps to fix my problem.

I need to have a long figure caption while maintaining the alignment of the rest of my document. I'd really appreciate if someone could help me figure this out.

Answer 1

The MWE you provide does not compile for me. When I create my own fig1.jpg (Should this really be a JPEG?) and change linewidth to \linewidth, I cannot reproduce the bug with TeX Live 2019.

The version of cas-dc.cls I have (2.1) loads stix as the math font and charis as the text font, which should both be scalable and work properly. If it can’t find charis, it loads stix as the text font too. It also looks for inconsolata as the fixed-width font, although that should not be causing the problem you have. You should make sure these packages are up-to-date. Are you getting warnings in your log file about them being missing?

If you are loading stix through your class file, it should not be necessary to also load either bm or amssymb, although neither will hurt.

PS

The actual document, unlike the MWE, was using a sans-serif font, and the class file does not load one. Loading any T1 sans-serif font would work.