Footnotes disappear when using overlays in beamer

The first slide has both footnotes instead of just the first one. This is less than ideal, but expected - you'll get the same result with \footfullcite.

On the second slide the citation commands are issued once more. The footnotes "disappear" because \ifciteseen returns true. Again this isn't what you want, but the result isn't surprising. The citation command can be modified to set a footnote for a given entry whenever \ifciteseen is false or its last footnote appeared on a previous overlay. The latter case is detected by equal frame numbers but different pages.

\documentclass{beamer}
\usepackage[english]{babel}
\usepackage{csquotes}
\usepackage[style=numeric-comp,citetracker=true,sorting=none,backend=biber]{biblatex}
\usepackage{hyperref}

\addbibresource{biblatex-examples.bib}

\makeatletter
\newtoggle{cbx@togcite}
% Citation number in brackets
\renewcommand\@makefntext[1]{%
  \iftoggle{cbx@togcite}
    {{\normalfont[\@thefnmark]}\enspace #1}
    {{\normalfont\@thefnmark}\enspace #1}%
  \global\togglefalse{cbx@togcite}}

\DeclareCiteCommand{\sfcite}[\cbx@superscript]%
  {\usebibmacro{cite:init}%
   \let\multicitedelim=\supercitedelim
   \iffieldundef{prenote}
     {}
     {\BibliographyWarning{Ignoring prenote argument}}%
   \iffieldundef{postnote}
     {}
     {\BibliographyWarning{Ignoring postnote argument}}}
  {\usebibmacro{citeindex}%
   \ifciteseen
     {\ifnumequal{\value{page}}{\csuse{cbx@page@\thefield{entrykey}}}
       {}
       {\ifnumequal{\value{framenumber}}{\csuse{cbx@frame@\thefield{entrykey}}}
          {\usebibmacro{sfcite}}
          {}}}
     {\usebibmacro{sfcite}}%
   \usebibmacro{cite:comp}}
  {}
  {\usebibmacro{cite:dump}}

\newbibmacro*{sfcite}{%
  \csnumgdef{cbx@page@\thefield{entrykey}}{\value{page}}%
  \csnumgdef{cbx@frame@\thefield{entrykey}}{\value{framenumber}}%
  \xappto\cbx@citehook{%
    \global\toggletrue{cbx@togcite}%
    \noexpand\footnotetext[\thefield{labelnumber}]{%
      \fullcite{\thefield{entrykey}}\addperiod}}}

\newrobustcmd{\cbx@superscript}[1]{%
  \mkbibsuperscript{\mkbibbrackets{#1}}%
  \cbx@citehook%
  \global\let\cbx@citehook=\empty}

\let\cbx@citehook=\empty
\makeatother

\begin{document}
\begin{frame}[b]
\frametitle{First Frame}
\begin{itemize}[<+->]
  \item First citation.\sfcite{reese} Recurrent citation.\sfcite{reese}
  \item Second citation.\sfcite{springer}
  \item Recurrent citation.\sfcite{springer}
\end{itemize}
\end{frame}

\begin{frame}[b]
\frametitle{Second Frame}
\begin{itemize}[<+->]
  \item Third citation.\sfcite{glashow}
  \item Recurrent citation.\sfcite{reese,springer,glashow}
\end{itemize}
\end{frame}

\begin{frame}[b]
\frametitle{Third Frame}
\begin{itemize}
  \item Recurrent citation.\sfcite{glashow}
  \item Recurrent citation.\sfcite{reese,springer,glashow}
\end{itemize}
\end{frame}

\end{document}

Here are the footnotes on the last slide from the first frame:

And the last slide of the second frame:

I had a similar issue that was solved in the following manner.

The citations disappear because each overlay is a new citation of the same cite, so, beamer is not the problem, indeed biblatex is. You have to check, for your special style (numeric-comp), how biblatex writes a new entry of a cited cite (i.e. ídem, ibidem, nothing, just a number). I use verbose style, so in the first citation biblatex writes the complete citation and uses the shorthand on the following. That's why changing citation to full instead of use of shorthand solve my problem. This last issue was solved using xpatch package.

In my case, preamble looks like:

\usepackage[style=verbose,autocite=footnote,notetype=footonly,babel=hyphen,backend=bibtex8]{biblatex}
\addbibresource{bibliography.bib}

\usepackage{xpatch}
\xpatchbibmacro{cite}{cite:short}{cite:full}{}{} 

\setbeamertemplate{footnote}{%
  \tiny%
  \parindent 1em\noindent%
  \raggedright
  \hbox to 1.8em{\hfil\insertfootnotemark}\insertfootnotetext\par%
}
\setlength\footnotesep{0pt}