Anchor point seems incorrect for Chemfig package

I'm trying to use chemfig to draw a basic schematic for enzymatic browning and have encountered a problem. In the bottom reaction (bottom right to bottom left) quinone is formed by the enzyme (denoted by the bracket underneath). The anchor for the curved arrow, however, seems to be incorrectly placed and try as I might I have not been able to solve the problem. I've tried flipping it every which way to no avail. Any tips?

\documentclass{article}

\usepackage{chemfig}
\setatomsep{2em}
\setbondoffset{0.5pt}
\setarrowdefault{,1.5,}

\begin{document}

\begin{figure}
\schemedebug{true}
\schemestart
\arrow{-U>[*{0.0}{\chemfig{O_2}, \chemfig{H_2O}}]}[90,2]
\chemup.\chemfig{N-[:30]Cu(-[:150]N)(-[:90,,,2,]H_2O)-[:30]O-O-[:-30]Cu(-[:90]OH_2)(-[:30]N)-[:-30]N}\chemdown]
\arrow{-U>[\chemfig{**6([,0.5]----(-OH)--)}][\chemfig{H_2O}]}[0]
\chemup.\chemfig{N-[:30]Cu(-[:150]N)(-[:90]O-[:30]**6([,0.5]------))-[:30]O-O-[:-30]Cu(-[:90]OH_2)(-[:30]N)-[:-30]N}\chemdown]
\arrow{-U>[*{0.180}2\chemfig{H^+}][*{0.180}\chemfig{H_2O}]}[-90]
\chemup.\chemfig{N-[:30]Cu(-[:150]N)-[:30]O-[:90]**6([:60,0.5]-(-[:-90,1]O-[:-30,1]Cu(-[:30,1]N)-[:-30,1]N)-----)}\chemdown]
\arrow{-U>[][*{0.north}\chemfig{*6([:-30,0.5]-(=[:-120]O)-(=[:-60]O)-=-=)}]}[180,1.85]
\schemestop
\end{figure}

\end{document}


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