Hi Sylvain,
I introduced this bug here: Bugfix: Display connectivity graph with empty Atlas · brainstorm-tools/brainstorm3@e8d719f · GitHub
Trying to fix this problem: Cannot display as connectivity graph - #12 by usui22
I reverted the part that causes the issue you reported: Bugfix: Revert a buggy modification made in commit e8d719f · brainstorm-tools/brainstorm3@6514f17 · GitHub
Please update Brainstorm and try again.
Thanks for reporting this bug quickly!