当我将“tcolorbox”设置为可破坏时，会出现不理想的边界线

Question

当我制作易碎品时，出现了不理想的边界线（尽管它们看起来并不明显）tcolorbox（参见下图中的红色箭头）。我该如何去除它们？

这是 MWE。如果您能帮助我解决此问题，我将不胜感激。

\documentclass[a5paper,12pt]{book}
\usepackage[top=1.5cm,bottom=2cm,includehead=true,inner=2cm,outer=1.8cm]{geometry}
\usepackage{amsmath,amsthm,amssymb}
\usepackage{varwidth}
\usepackage[dvipsnames]{xcolor}
\usepackage[breakable,skins,theorems]{tcolorbox}
\tcbset{parbox=false,colback=white}
\newtcbtheorem[number within=chapter]{myexample}{Example}{breakable,enhanced,frame empty,interior empty,colframe=black!40,coltitle=black,fonttitle=\bfseries,colbacktitle=black!10,borderline={0.4mm}{0mm}{black!40},attach boxed title to top left={xshift=5mm,yshift=-2mm},boxed title style={boxrule=0.2mm},varwidth boxed title}{}


\begin{document}

\chapter{ff}

\section{ff}

\begin{myexample}{}{}
fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff 

fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff 

fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff 

fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff 

fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff fffff fffff fffffff 
\end{myexample}

\end{document}