Labeling Blocks will create a solid line about plotneuralnet

[omegahh]

My latex environment is Mactex 2017, does it matter?

[HarisIqbal88]

I tried to let the Box block's edges be invisible via fill=\fill, draw=\fill in Box.sty.

It does not make the edge invisible, it makes it the same colour as the fill. This is not important if opacity is high, but try with a low opacity and you get your edges visible.

Finally I found that \path (b) edge ["\bf\xlabel"', midway] (c); created a solid line in BC, so do AB and CF.

Yes, in my code every edge that is there to create a label(except for caption) also creates a line.

I don't know why the solid lines emerged though no pic action acted in above code.

As far as I understand, it is the default behaviour of the edge which you will notice if you run the code below. If you want to remove edges, I can think of 2 ways:

\documentclass[border=15pt, multi, tikz]{standalone}
\usetikzlibrary{quotes}

\begin{document}
\begin{tikzpicture}
% With Visible Edge 
\path (0,0,0) edge["Some text 1."',pos=0.5,text width=50,text centered] (4,0,0); 
% With edge opacity=0
\path (0,1,0) edge["Some text 2."',pos=0.5,text width=50,text centered, opacity=0, text opacity=1] (4,1,0); 
% With edge between 1 node
\path (0,2,0) edge["Some text 3."',text width=50,text centered] (0,2,0);
 
\end{tikzpicture}
\end{document}

[omegahh]

Yes, your replies help me a lot. Thanks!