The general approach from Sorting citations using \cites command in biblatex can still be used. But it needs updating again.
In Audrey's original code replace
\def\cbx@sortkeysinit{%
\ifcsundef{blx@sort@\the\c@refsection}
{\global\letcs{\cbx@sortkeys}
{blx@slists@\the\c@refsection @entry@\blx@sorting}}% Biber
{\global\letcs{\cbx@sortkeys}{blx@sort@\the\c@refsection}}}% BibTeX
with
\def\cbx@sortkeysinit{%
\ifcsundef{blx@dlist@entry@\the\c@refsection @\blx@refcontext@context}
{}
{\global\csletcs{cbx@sortkeys}{blx@dlist@entry@\the\c@refsection @\blx@refcontext@context}}}
Then everything should work as advertised again
\documentclass{article}
\usepackage[style=authortitle,sorting=ynt,sortcites]{biblatex}
\makeatletter
% original definition of \cites
\DeclareMultiCiteCommand{\cbx@cites}{\cite}{\multicitedelim}
% new definition
\DeclareMultiCiteCommand{\cites}[\cbx@cite@wrapper\cbx@cites]{\cbx@cite}{}
% first pass saves keys, prenotes, postnotes
\DeclareCiteCommand{\cbx@cite}
{\csxdef{prenote:\thefield{entrykey}}{\thefield{prenote}}}
{\listxadd\cbx@savekeys{\thefield{entrykey}}}
{}
{\csxdef{postnote:\thefield{entrykey}}{\thefield{postnote}}}
% second pass outputs sorted citation list
\newrobustcmd{\cbx@cite@wrapper}[2]{%
\def\cbx@savekeys{}%
\def\cbx@citecall{#1}%
#2\cbx@sortkeysinit\cbx@citesort\cbx@citecall}
% internal list of saved keys => sorted argument list
\def\cbx@citesort{%
\def\do##1{%
\ifinlist{##1}{\cbx@savekeys}
{\protected@xappto\cbx@citecall{%
[\csuse{prenote:##1}][\csuse{postnote:##1}]{##1}}}
{}}%
\dolistloop{\cbx@sortkeys}}
% internal list of sorted entry keys
\def\cbx@sortkeysinit{%
\ifcsundef{blx@dlist@entry@\the\c@refsection @\blx@refcontext@context}
{}
{\global\csletcs{cbx@sortkeys}{blx@dlist@entry@\the\c@refsection @\blx@refcontext@context}}}
\def\cbx@sortkeys{}
\makeatother
\addbibresource{biblatex-examples.bib}
\newcommand{\cmd}[1]{\texttt{\textbackslash #1}}
\setlength{\parindent}{0pt}
\begin{document}
\cmd{cite}: \cite{companion,ctan,vangennep,markey} \\
\cmd{cites}: \cites[e.g.][10]{companion}{ctan}{markey}[10--11]{vangennep} \\
\cmd{Cites}: \Cites{ctan}{markey}[e.g.][5--10]{companion}[10--11]{vangennep}
\printbibliography
\end{document}

I also tried copying the whole example in new blank document. No success there also..
– tingdling Mar 19 '18 at 14:45biblatex. I have added an answer with the required change. – moewe Mar 20 '18 at 10:26