The file
\documentclass{article}
\usepackage{fontspec}
\setmainfont[Ligatures=TeX]{MinionPro}
\setsansfont[Ligatures=TeX]{CronosPro}
\begin{document}
MinionPro: \textbf{bold}
\textsf{CronosPro: \textbf{{bold}}}
\end{document}
run through lualatex from TeXLive-2015 gives a PDF file as expected; with lualatex from TeXLive-2016, MinionPro bold is displayed as expected, but for CronosPro, BoldItalics is used instead. I'd be happy to provide the logs if a kind soul would like to look into this strange change.