Hi Long, it apparently fixed the issue : the field group meta box does not appear anymore where it is not supposed to.
Am I right to assume that you fixed it by manually adding "post" to "post_types" ? Was there a corruption of the code that removed the post type, causing the meta box to appear in unusual places ?
"meta_box": {
"title": "Médias-Photos-Fields",
"id": "medias-photos",
"post_types": [
"post"
Thanks a ton for your help anyways !