I finally did some new tests and it works a lot, even in z2m, great!
However, there is still a space that gets added at the end of the variable you insert:
And this space messes up the json sent to z2m which receives a bad message →
z2m: Invalid message 'undefined', skipping...
So you must absolutely remove this space between the variable and the comma and then everything works correctly.
I will create an improvement request.
EDIT: [Scènes] supprimer l'espace inséré automatiquement après l'appel d'une variable