[Tex/LaTex] Beamer Metropolis theme overfull vbox error on title page

beamerbeamer-metropolispdftexwarnings

I'm trying to make slides for a course I'm teaching this coming semester using beamer and I have a nagging issue with an overfull vbox that I can't diagnose when using the metropolis theme. Here is the minimal example. Note, I'm using pdflatex (for microtype features):

% !TEX program = pdflatex
% !TEX spellcheck = en_US

\documentclass[aspectratio=169]{beamer}

% Font Settings

\usepackage[english]{babel}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[autostyle,english=american]{csquotes}
\usepackage[sfdefault,scaled=0.85,lf]{FiraSans}
\usepackage[scaled=0.85]{FiraMono}
\usepackage{newtxsf}
\usepackage[protrusion,expansion,kerning,spacing,final]{microtype}
\microtypecontext{spacing=nonfrench}

% PDF Bookmarks

\usepackage{bookmark}

% Beamer Setup

\usetheme{metropolis}
\usecolortheme{owl}

% AMS Math Packages

\usepackage{amsmath}

\title{A minimal example}
\date{\today}
\author{Matthias Vogelgesang}
\institute{Centre for Modern Beamer Themes}
\begin{document}
    \maketitle %<-- here is where i get an "Overfull \vbox (15.63992pt too high)"
    \section{First Section}
    \begin{frame}{First Frame}
        Hello, world!
    \end{frame}
\end{document}

I basically pulled this example from the package documentation but included my own preamble. To my knowledge I have the current version of all packages except for babel (which is at 3.18 on my system).

Best Answer

The theme is not very careful regarding spurious spaces. If one removes the one from the titlepage definition the warning disappears (but there are more ...):

\documentclass[aspectratio=169]{beamer}

% Font Settings

\usepackage[english]{babel}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[autostyle,english=american]{csquotes}
\usepackage[sfdefault,scaled=0.85,lf]{FiraSans}
\usepackage[scaled=0.85]{FiraMono}
\usepackage{newtxsf}
\usepackage[protrusion,expansion,kerning,spacing,final]{microtype}
\microtypecontext{spacing=nonfrench}

% PDF Bookmarks

\usepackage{bookmark}

% Beamer Setup

\usetheme{metropolis}
\usecolortheme{owl}

% AMS Math Packages

\usepackage{amsmath}

\title{A minimal example}
\date{\today}
\author{Matthias Vogelgesang}
\institute{Centre for Modern Beamer Themes}
\def\titlepage{%
  \usebeamertemplate{title page}%<---
}
\begin{document}
    \maketitle %<-- here is where i get an "Overfull \vbox (15.63992pt too high)"

    \section{First Section}
    \begin{frame}{First Frame}
        Hello, world!
    \end{frame}
\end{document}
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