Message à l'ouverture de certains fichiers Illustrator sur les paramètres de couleur

You need to set up your color management accordingly.

Open Edit > Color settings and set it to the Secure CMYK workflow by setting it up to ignore color profiles. This setting was used when the document has been created. And also this setting prevents black from getting converted.

You might also want to check the documents you have recently opened whether or not black is still clean.