Hello François,
Thanks for reaching out.
I understand that there are 2 issues in your screen record:
1. You update the field group ID and Meta Box creates a new local JSON file under the mb-json folder.
2. You disable the field group but the fields still display on the editing page.
Both of them are expected and work as they are. If you change the field group ID, Meta Box will create a new JSON file based on the new ID. The JSON file will be deleted if you delete the field group with UI. Otherwise, you need to delete the JSON file in the folder mb-json manually.
Second thing, there is a note in the documentation https://docs.metabox.io/local-json/#syncing-changes
Syncing from JSON to the database has only one purpose: to edit fields visually, and then sync back to JSON files (or export to JSON file to save somewhere else). Meta Box will NOT load fields from the database (to avoid making unnessary queries), and use JSON files only.
That means Meta Box will load fields from JSON files, not from the UI field group in this case.
.
