Warum wird die Jahreszahl bei pgfplots plötzlich als Float ausgegeben?

\documentclass{standalone}

\usepackage{pgfplots}
\usepackage{pgfplotstable}
\usetikzlibrary{shapes,arrows, positioning}

\begin{document}
\begin{tikzpicture}
  \begin{axis}[
    height=4cm,
    width=\textwidth,
    ybar,
    xmin = 1984, xmax = 2022,
    ymin = 0, ymax = 3.5,
    xtick={1985,...,2021},
    x tick label style={rotate=90, anchor=east, /pgf/number format/1000 sep=},
    xtick pos=left,
    ylabel={Number of failures},
    ytick={0,...,3},
    bar width = 5pt
]
  \addplot coordinates {
        (1985, 3)
        (1986, 0)
        (1987, 0)
        (1988, 0)
        (1989, 0)
        (1990, 0)
        (1991, 0)
        (1992, 0)
        (1993, 0)
        (1994, 0)
        (1995, 0)
        (1996, 0)
        (1997, 0)
        (1998, 0)
        (1999, 2)
        (2000, 0)
        (2001, 0)
        (2002, 0)
        (2003, 0)
        (2004, 0)
        (2005, 0)
        (2006, 0)
        (2007, 0)
        (2008, 0)
        (2009, 0)
        (2010, 0)
        (2011, 0)
        (2012, 0)
        (2013, 0)
        (2014, 0)
        (2015, 0)
        (2016, 0)
        (2017, 0)
        (2018, 0)
        (2019, 0)
        (2020, 0)
        (2021, 0)
        (2013, 1)
  };
  \end{axis}
\end{tikzpicture}
\end{document}