LaTeX-fill-paragraph problem

[Erwan Hingant]

Hello All,

 Hope to be to the right place (if not let me know). I have a trouble
 with a minimal configuration of emacs with auctex when filling a
 commented line. Indeed, when I use M-q on to the commented line in the
 text below:

\documentclass{standalone}

\begin{document}
 % \[a=b=a=b=a=b=a=b=a=b=a=b=a=b=a=b=a=b =  
a=b=a=b=a=b=a=b=a=b=a=b=a=b=a=b=a=b=a=b=\]
\end{document}

I have a kind of infinite loop that I have to stop with C-g and then
show an amount of % like

 %
 %
 .
 .
 .
 %
 %
 %
 % \[a=b=a=b=a=b=a=b=a=b=a=b=a=b=a=b=a=b =  
a=b=a=b=a=b=a=b=a=b=a=b=a=b=a=b=a=b=a=b=\]

where dots means a lot of similar line. Without comment I have a nice
filling like:

 \[a=b=a=b=a=b=a=b=a=b=a=b=a=b=a=b=a=b =
   a=b=a=b=a=b=a=b=a=b=a=b=a=b=a=b=a=b=a=b=\]

I have very infructuous search on internet and only found the
documentation which mention possible error but with
LaTex-fill-environment at
https://www.gnu.org/software/auctex/manual/auctex/Filling.html

I am very new to emacs and auctex, so I ask for your kind help and I
stay aware if any aditional information is necessary.

Sincerely,
Erwan.