Nested Repeater Fields with Pagination Enabled Do Not Save Correctly

Comienza con el JSON de Repeater anidado proporcionado y reproduce el flujo de guardado en el backend de WordPress usando paginación en ambos campos Repeater. Compara los valores anidados antes de guardar y después de volver a abrir la página; se considera terminado cuando el contenido del Repeater interno se conserva y se muestra correctamente. En la issue no se menciona ningún archivo fuente ni ninguna prueba, por lo que localizar la ruta de guardado relevante y añadir cobertura de regresión requerirá investigar el proyecto.

Describe the bug
When two nested ACF fields (both of type Repeater) have the option "pagination": 1 enabled, the inner field content is no longer saved correctly. The data appears to be lost or overwritten during save.

To Reproduce
Steps to reproduce the behavior:

1. Create a Repeater field (Parent Repeater).
2. Inside this field, add another Repeater field (Child Repeater).
3. Enable "pagination": 1 for both Repeater fields.
4. Add content to both fields in the WordPress backend.
5. Save the post.
6. Reopen the post and check the values — the inner Repeater content is missing or not saved correctly.

Expected behavior
The values entered in both nested Repeater fields (with pagination enabled) should be saved and displayed correctly after saving the post.

Screenshots or Video
N/A — the issue is data-related and occurs upon save.

Code
You will find attached the exported JSON of the relevant ACF field group that reproduces the issue. (Attach your JSON export when submitting the ticket.)

Version Information:

• WordPress Version: 6.8.1
• ACF PRO Version: 6.4.2
• PHP Version: 8.1.x
• Browser: Chrome (latest)

JSON:

{
    "key": "group_5e67884841724",
    "title": "Fieldgroup XYZ",
    "fields": [
        {
            "key": "field_5e67889ad8b2a",
            "label": "Flexible Content",
            "name": "flexible_content",
            "aria-label": "",
            "type": "flexible_content",
            "instructions": "",
            "required": 0,
            "conditional_logic": 0,
            "wrapper": {
                "width": "",
                "class": "",
                "id": ""
            },
            "allow_in_bindings": 0,
            "wpml_cf_preferences": 2,
            "admin_only": 0,
            "exclude_customer": 0,
            "layouts": {
                "layout_6604371afv5cd7": {
                    "key": "layout_6604371afv5cd7",
                    "name": "layout_xyz",
                    "label": "Layout XYZ",
                    "display": "block",
                    "sub_fields": [
                        {
                            "key": "field_68042e0594df7",
                            "label": "Repeater 1",
                            "name": "repeater_1",
                            "aria-label": "",
                            "type": "repeater",
                            "instructions": "",
                            "required": 0,
                            "conditional_logic": 0,
                            "wrapper": {
                                "width": "",
                                "class": "",
                                "id": ""
                            },
                            "allow_in_bindings": 0,
                            "wpml_cf_preferences": 2,
                            "admin_only": 0,
                            "exclude_customer": 0,
                            "collapsed": "",
                            "pagination": 0,
                            "min": 1,
                            "max": 0,
                            "layout": "block",
                            "button_label": "Add Item Repeater 1",
                            "rows_per_page": 20,
                            "sub_fields": [
                                {
                                    "key": "field_66265bd4e88e9",
                                    "label": "Repeater 2",
                                    "name": "repeater_2",
                                    "aria-label": "",
                                    "type": "repeater",
                                    "instructions": "",
                                    "required": 0,
                                    "conditional_logic": 0,
                                    "wrapper": {
                                        "width": "",
                                        "class": "",
                                        "id": ""
                                    },
                                    "allow_in_bindings": 0,
                                    "admin_only": 0,
                                    "exclude_customer": 0,
                                    "collapsed": "",
                                    "pagination": 0,
                                    "min": 1,
                                    "max": 10,
                                    "layout": "row",
                                    "button_label": "Add Item Repeater 2",
                                    "rows_per_page": 20,
                                    "parent_repeater": "field_68042e0594df7",
                                    "sub_fields": [
                                        {
                                            "key": "field_662b9e12d3a7f",
                                            "label": "Media-File",
                                            "name": "media_file",
                                            "aria-label": "",
                                            "type": "file",
                                            "instructions": "",
                                            "required": 1,
                                            "conditional_logic": 0,
                                            "wrapper": {
                                                "width": "50",
                                                "class": "",
                                                "id": ""
                                            },
                                            "allow_in_bindings": 0,
                                            "wpml_cf_preferences": 2,
                                            "admin_only": 0,
                                            "exclude_customer": 0,
                                            "return_format": "array",
                                            "preview_size": "thumbnail",
                                            "library": "all",
                                            "min_width": "",
                                            "min_height": "",
                                            "min_size": "",
                                            "max_width": "",
                                            "max_height": "",
                                            "max_size": "",
                                            "mime_types": "mp3",
                                            "parent_repeater": "field_66265bd4e88e9"
                                        }
                                    ]
                                }
                            ]
                        }
                    ],
                    "min": "",
                    "max": ""
                }
            },
            "button_label": "",
            "min": "",
            "max": ""
        }
    ],
    "location": [
        [
            {
                "param": "post_type",
                "operator": "==",
                "value": "page"
            }
        ]
    ],
    "menu_order": 1,
    "position": "normal",
    "style": "default",
    "label_placement": "top",
    "instruction_placement": "label",
    "hide_on_screen": "",
    "active": true,
    "description": "",
    "show_in_rest": 0,
    "modified": 1750158065
}