I don’t know about wrong results, but compare Godement’s Algèbre (1966, and still 1980):
on dit que l’ensemble $x\mathrm H$ est une classe à droite modulo $\mathrm H$
Translation: we say that the set 𝑥H is a class on the right modulo H
with everyone else, e.g. his associate Bourbaki (1970):
les ensembles $x\mathrm H$, qu'on appelle classes à gauche suivant $\,\mathrm H$ (ou modulo $\,\mathrm H$)
Translation: the sets 𝑥H, which are called classes on the left following H (or modulo H)
