documentclass{article}
usepackage{amsmath}
usepackage{fontspec}
usepackage{unicode-math}
setmathfont{xits-math.otf}
setmathfont[range=up/{latin,Latin,num}]{XCharter-Roman.otf} % extra character appears between two lines
%setmathfont[range=up/{latin,Latin,num}]{Charis SIL}  % extra character appears between two lines
%setmathfont[range=up/{latin,Latin,num}]{texgyretermes-regular.otf}  % works okay with this
%setmathfont[range=up/{latin,Latin,num}]{Times}  % works okay with this
begin{document}
begin{equation*}
  x = begin{cases}
  y \  y
    end{cases}
end{equation*}
end{document}