std value in nested group doesn't work

Hi,

I’m using the following group configuration:

//GROUPES MEDICAMENTS
            [
                'type' => 'group',
                'tab' => 'medicaments',
                'id' => 'liste_medicaments',
                'clone' => true,
                'add_button' => '+ Ajouter un nouveau médicament',
                'sort_clone' => true,
                'collapsible' => true,
                //'save_state' => true, //Whether or not save the collapse/expand state?
                'default_state'	=> 'collapsed', // or expanded (default).
                'group_title' => 'Indication(s) {#} {medicament}',
                'required'    => 1,
                'fields' => [
                    [
                        'type' => 'group',
                        'id' => 'medicaments',
                        'clone' => true,
                        'add_button' => '+ Ajouter une ligne de médicament',
                        'required'    => 1,
                        'fields' => [
                            [
                                'name' => __( 'Médicament', 'earlytrack' ),
                                'id' => 'medicament',
                                'type' => 'text',
                                'columns' => 5,
                            ],
                            [
                                'name' => __( 'Dosage', 'earlytrack' ),
                                'id' => 'dosage',
                                'type' => 'text',
                                'columns' => 5,
                            ],
                            [
                                'name' => __( 'Code UCD', 'earlytrack' ),
                                'id' => 'code_ucd',
                                'type' => 'text',
                                'columns' => 2,
                            ],
                        ],
                    ],
                    [
                        'name' => __( 'Statut', 'earlytrack' ),
                        'id' => 'statut',
                        'type' => 'radio',
                        'options' => [
                            'AAP' => __( 'AAP', 'earlytrack' ),
                            'AAC très précoce' => __( 'AAC très précoce', 'earlytrack' ),
                            'CPC' => __( 'CPC', 'earlytrack' ),
                            'Autre' => __( 'Autre', 'earlytrack' ),
                        ],
                        'columns' => 6,
                    ],
                    //SI AUTRE
                    [
                        'name' => __('Préciser le statut (Autre)', 'earlytrack'),
                        'id' =>'autre_statut',
                        'type' => 'text',
                        'columns' => 6,
                        'visible' => [
                            'when' => [
                                ['statut', '=', 'Autre'],
                            ],
                        ],
                    ],
                    [
                        'name' => __( 'Date d\'obtention', 'earlytrack' ),
                        'id' => 'date_obtention',
                        'type' => 'html5_date',
                        'date_type' => 'date',
                        'columns' => 12,
                    ],
                    [
                        'name' => __( 'Indication(s)', 'earlytrack' ),
                        'id' => 'indications',
                        'type' => 'textarea',
                        'columns' => 12,
                    ],
                    [
                        'name' => __( 'Nombre annuel de visites de suivi prévu au PUT', 'earlytrack' ),
                        'desc' => __( 'et autres indications, si nécessaire', 'earlytrack' ),
                        'id' => 'nombre_visites',
                        'type' => 'textarea',
                        'columns' => 6,
                    ],
                    [
                        'name' => __( 'Type de suivi', 'earlytrack' ),
                        'id' => 'type_suivi',
                        'type' => 'radio',
                        'options' => [
                            200 => __( 'Modéré (≤ 2 visites)', 'earlytrack' ),
                            500 => __( 'Soutenu (≥ 3 visites)', 'earlytrack' ),
                        ],
                        'columns' => 6,
                    ],

                ],
                'std' => get_post_meta( $nom_etude, 'liste_medicaments', true ) ?: [],
            ],

As you can see on the last line, I’m setting the std value from a get_post_meta() call, coming from another frontend form, directly on the liste_medicaments group. (For context, $nom_etude is populated from $_GET['nom_etude'] and is working correctly with other forms.)

The top-level std is applied as expected (it creates the correct number of liste_medicaments clones based on the initial form), but the nested group medicaments inside liste_medicaments is no longer populated with the saved data.

This used to work fine with Meta Box AIO v2, but it stopped working from v3.0.1 onward. I waited for newer releases in case it was a bug, but even with v3.3.4 the behaviour is still the same.

Could you please help me understand whether this is a regression, a breaking change in how std works with nested/cloneable groups, or if there’s now a different recommended way to pre-populate a nested group from get_post_meta()?