Expression error or bug?

I don't understand something, and I don't know if I'm dumb or if it's a bug.

I have a layer with a lot of effects on it (for making procedural gears). I use a lot of expressions and effects on it. But one of them (to get the scale from a transform effect) triggers an error:

(In French): After Effects (alerte): Expression désactivée. Erreur à la ligne 1 : Propriété ou méthode nomée "Echelle" dans la classe "group" introuvable ou inexistante; elle a peut-être été renomée, déplacée ou supprimée, ou le nom est mal orthographié.  ///  Expression disabled. Error on line 1: Property or method named "Echelle" in the "group" class not found or does not exist; it may have been renamed, moved, or deleted, or the name is misspelled.

BUT it is the good name. I've checked the typing and also used the expression picker to be sure, but it just doesn't work on its own layer. I tried the other expressions on the same layer and I get the same issue with each of them.

BUT if I call the exact same effect from another comp, it works. So I don't get it.

I've tried different typings like:

effect("Sandwich Transformation 2")("Echelle")
or

thisComp.layer("Calque de forme 39").effect("Sandwich Transformation 2")("Echelle")

But nothing seems to work. 

I'm on the last 25.1