A wrapfigure on the left side of the page interferes with the mechanism that marginnote
uses to determine horizontal position, pushing it to the right by the width of the wrapfigure.
The marginnote
package has the macros \marginnoteleftadjust
and \marginnoterightadjust
for custom horizontal adjustment, but I haven't had any luck getting these to move the notes at all.
\documentclass{article}
\usepackage{wrapfig}
\usepackage{marginnote}
\usepackage{lipsum}
\usepackage{graphicx}
\begin{document}
\begin{wrapfigure}[8]{L}{3cm}
\includegraphics[width=3cm]{example-grid-100x100pt}
\end{wrapfigure}
Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Ut purus elit, vestibulum ut, placerat ac, adipiscing vitae, felis. Curabitur dictum
\marginnote{This margin note is too far right}
\lipsum[1-2]
\marginnote{This one is not too far right}
\lipsum[3]
\end{document}