Weird letter ‘i’ in the reference frame title in beamer

Question

I am preparing a beamer presentation and when I add a reference and compile it the title of References frame gets and an extra letter 'i'. What is the problem here? see below my code.

Thanks.

\documentclass{beamer}
\usepackage{xcolor}
\definecolor{uuc}{rgb}{0.76,0.24,0.13}
\usepackage{tikz}
\usepackage[citestyle=authoryear]{biblatex}
\addbibresource{bibo.bib}

%%%%%%%%%%% Title
\title{Title}
\subtitle{Subtitle}
\author{Author}
\date{}
\institute{Institute}
%%%%%%%%%%%%%%
\useoutertheme[progressbar=frametitle]{metropolis}
 \setbeamertemplate{frame numbering}[fraction]
\useoutertheme{metropolis}
\useinnertheme{metropolis}
\usefonttheme{metropolis}
\usecolortheme[named=uuc]{structure}

\begin{document}
\maketitle

\begin{frame}[t]{Title}
Hello, world!\footcite{ref1}
\end{frame}


\begin{frame}[allowframebreaks, plain,noframenumbering]{References}
\printbibliography[heading = none]  
 \end{frame}

  \end{document}

Answer 1

The i is in fact a roman number 1; the confusion comes from it being capitalised and in a sans serif font. On the next continuation slide i will be replaced by ii, and so on.

You can turn this numbering off with

\setbeamertemplate{frametitle continuation}{}

for example just before the relevant frame(s):

\documentclass{beamer}

\usepackage{lipsum}% for dummy text

\begin{document}

\begin{frame}[allowframebreaks]
  \frametitle{Numbered continuation frames}

  \lipsum[1-2]
\end{frame}

\setbeamertemplate{frametitle continuation}{}
\begin{frame}[allowframebreaks]
  \frametitle{Unnumbered continuation frames}

  \lipsum[1-2]
\end{frame}

\end{document}

Confusingly the noframenumbering option refers to something else, namely frame numbers throughout the document that are often used in footers.