When I try to compile this MWE in Overleaf (although I should rather say "minimal non-working example"):

```
\documentclass[12pt,reqno]{amsart}

\title{Title}
\author{\normalsize John Doe}

\begin{document}

\maketitle

\end{document}

```

I get the following errors:

[![enter image description here](https://i.stack.imgur.com/idFnO.png)](https://i.stack.imgur.com/idFnO.png)

However, the code compiles correctly as expected if instead we substitute `\normalsize` by `\tiny`, `\scriptsize`, `\footnotesize`, `\small`, `\large`, `\LARGE`, `\huge` or `\HUGE`. So what is happening?