Non è tanto titlsec ma hyperref. Soluzione ❓
usare \phantomsection.
`\documentclass{book}
%\usepackage[italian]{babel}
\usepackage{gchords}
\usepackage[margin=3cm,top=3cm,bottom=3cm]{geometry}
\usepackage{guitar}
\usepackage{sectsty}
\usepackage{titlesec}
\usepackage{multicol}
\usepackage{hyperref}
\pagestyle{plain}
\setlength{\columnsep}{.25in}
\titlespacing{\section}{0pt}{*0}{*0}
\begin{document}
\tableofcontents
\clearpage
\phantomsection
\section*{Misunderstood \\ \textmd{\textsc{\large{Bon Jovi}}}}
\addcontentsline{toc}{section}{Misunderstood – \textsc{Bon Jovi}}
\clearpage
\phantomsection
\section*{Always \\ \textmd{\textsc{\large{Bon Jovi}}}}
\addcontentsline{toc}{section}{Always – \textsc{Bon Jovi}}
\end{document} `
e togli sectsty, usa solo titlesec.
Ciao
Andrea