Advanced Rules → Add Rule button non-functional

Hi,

Thank you for the reply. Here is the JSON contents:

{
    "$schema": "https://schemas.metabox.io/field-group.json",
    "context": "side",
    "fields": [
        {
            "type": "select",
            "id": "post_display_order",
            "name": "Post Display Order",
            "size": 3,
            "admin_columns": {
                "position": "before date",
                "sort": "numeric"
            },
            "tooltip": {
                "content": "Order of the post in the <a href=\"/news\">News</a> page."
            },
            "std": 99,
            "options": {
                "99": "Default",
                "01": "1",
                "02": "2",
                "03": "3",
                "04": "4",
                "05": "5",
                "06": "6",
                "07": "7",
                "08": "8",
                "09": "9"
            },
            "datalist": {
                "id": "68c0cafec953a",
                "options": [
                    "01",
                    "02",
                    "03",
                    "04",
                    "05",
                    "06",
                    "07",
                    "08",
                    "09"
                ]
            }
        }
    ],
    "id": "post-fields",
    "modified": 1757465342,
    "title": "Post fields"
}

It works as expected when I import this into a demo site. On the "broken" site deactivating all other plugins except Meta Box AIO did not help.