Bad vertical spacing in multicol

Question

Issue

First, I'm sorry: I didn't manage to produce a MWE. I hope some of you will still be able to help.

I use the multicol package to create list of exercises. An exercise is an environment which is within a minipage (to prevent column breaks). Something like

\newenvironment{exo}
{\begin{minipage}{\columnwidth}}
{\end{minipage}}

Quite often, the first exercise of a new column is not aligned with the top of the column:

Idea 1

I have noticed that putting \setlength{\topskip}{0pt} helps a lot but still, it is not perfectly aligned.

Idea 2

Quite surprisingly, I change \begin{minipage}{\columnwidth} to \begin{minipage}{0.97\columnwidth} (in the current example), the issue disappears:

Idea 3

If I delete the newlines between two exercise environments (in the source), the problem disappears but that makes the source file less readable:

\begin{exercise}
bla bla bla
\end{exercise}
\begin{exercise}
bla bla bla
\end{exercise}

Question

So, do you have any hint?

File

The source files (not MWE at all) are there https://we.tl/Hbap24qlw2

Answer 1

The problem doesn't come from the multicol environment, it comes from the minipage environment that adds a space before.

The removal of the space located before the minipage environment is given in this response: How to reduce space before minipage

You can undo either of these vertical spaces by issuing \vspace{-\parskip} or \vspace{-\abovedisplayskip} just before the minipage.

Just delete the space before the minipage environment, which is before begin{exo}:

\vspace{-\abovedisplayskip}
\vspace{-\parskip}
\begin{exo} 
Vous voulez acheter un billet de loterie. Le buraliste,
logicien à ses heures perdues, vous en présente cinq numérotés de 1
à 5, et vous déclare :
\begin{itemize}
 \item si 5 est perdant, alors 1 est gagnant ;  
\item si 4 est perdant, alors 2 est gagnant ;    
 \item si 3 est perdant, alors 5 aussi ;    
 \item si 1 est gagnant, alors 2 aussi ;    
 \item si 3 est gagnant, alors 4 est perdant.
\end{itemize}
%\noindent 
Quel billet choisissez-vous ?

\end{exo}