There's a nice workaround for the titlesec/nameref conflict here but I'm finding it doesn't work for the memoir class. Below is my MWE that works for the book class.
\documentclass{book}
% \documentclass{memoir}
\usepackage{titlesec}
\usepackage{hyperref}
\makeatletter
\newcommand\setcurrentname[1]{\def@currentlabelname{#1}}
\newcommand{\labelledsection}[2]{\section*{#1}\setcurrentname{#1}\label{#2}}
\makeatother
\begin{document}
\chapter*{Unnumbered Chapter}\setcurrentname{Unnumbered Chapter}\label{chap:unnumbered}
\labelledsection{Unnumbered Section}{sec:unnumbered}
Check \nameref{sec:numbered}.
\chapter{Numbered Chapter} \label{chap:numbered}
\section{Numbered Section} \label{sec:numbered}
Check \nameref{sec:unnumbered}.
\end{document}
The MWE generates text that correctly refs the section:
But if I switch to the memoir class it refs the chapter?:

