I have stripped down to the following MWE after some experimentation. As it is, it works without any problems.
\documentclass{memoir}
\usepackage[ocgcolorlinks]{hyperref}
\usepackage{tikz}
\usetikzlibrary{patterns}
\author{The author}
\title{Some title}
\begin{document}
\frontmatter
\maketitle
\listoffigures
\mainmatter
\chapter{first}
\section{first}
Some figure
\begin{figure}%
\centering
\begin{tikzpicture}
\draw[fill,pattern=north east lines,thick] (0,0) rectangle (5cm,2cm);
\end{tikzpicture}
\caption{Some caption}%
\label{fig:a1}%
\end{figure}
\end{document}
Notice the coloring and the weight of the font on LoF entries:

But when I change the location of the hyperref declaration to somewhere after TikZ and its library declaration, the whole figure environment just vanishes (but LoF still knows that it's there) also LoF entry loses its color(I guess!).

If I remove the patterns library dependence (fill=yellow or anything else) the second picture above is obtained and the TikZ picture is rendered correctly regardless of the declaring order. This suggests that the second image is the correct one and something fishy is going on either in the pattern library or ocgcolorlinks option. Does anyone know why? Or is it a bug?