ref command not working in the argument of redefined section/subsection command (UAI template)

The class has broken section somehow. You should report it to the maintainers.

However a simple workaround seems to be to move label

documentclass{uai2021}

begin{document}

section{zzz}label{abc}
aaa see Section~ref{abc}
end{document}

with label after the argument produces

with it in the argument

documentclass{uai2021}

begin{document}

section{zzzlabel{abc}}
aaa see Section~ref{abc}
end{document}

Gives the error

! Undefined control sequence.
label #1->@bsphack begingroup def label@name 
                                                  {#1}label@hook protected...
l.5 section{zzzlabel{abc}}
                            
? 

---

The issue can be simplified down to files just in standard distributions

documentclass{article}

usepackage{titlesec}
titleformat*{section}{MakeUppercase}

begin{document}

section{zzzlabel{abc}}
aaa see Section~ref{abc}
end{document}

gives the error

! Missing control sequence inserted.
<inserted text> 
                inaccessible 
l.8 section{zzzlabel{abc}}
                            
?