Block preview with group or repeater field not working

Since ACF 5.11 fixed a security issue with acf_get_value() function, checking if field really exists, passing example data in acf_register_block_type() for group of repeater field does not work anymore.

Example block fields

"fields": [
{
  "key": "field_6183b15180469",
  "label": "Text left",
  "name": "text_left",
  "type": "group",
  "instructions": "",
  "required": 0,
  "conditional_logic": [
      [
          {
              "field": "field_6183ae54e27bc",
              "operator": "==",
              "value": "text"
          }
      ]
  ],
  "wrapper": {
      "width": "50",
      "class": "",
      "id": ""
  },
  "layout": "block",
  "sub_fields": [
      {
          "key": "field_6183b17b8046a",
          "label": "Title",
          "name": "text_title",
          "type": "text",
          "instructions": "",
          "required": 0,
          "conditional_logic": 0,
          "wrapper": {
              "width": "",
              "class": "",
              "id": ""
          },
          "default_value": "",
          "placeholder": "",
          "prepend": "",
          "append": "",
          "maxlength": ""
      },
      {
          "key": "field_6183b19b8046b",
          "label": "Text",
          "name": "text",
          "type": "wysiwyg",
          "instructions": "",
          "required": 0,
          "conditional_logic": 0,
          "wrapper": {
              "width": "",
              "class": "",
              "id": ""
          },
          "default_value": "",
          "tabs": "all",
          "toolbar": "full",
          "media_upload": 1,
          "delay": 0
      }
  ]
  }
]

In version 5.10 we would pass the example data as follows

[
 'text_left' => [
    'text_title' => 'Lorem ipsum dolor',
    'text'       => 'Pellentesque tincidunt nulla nisi, eget vehicula turpis tincidunt ut. Fusce pharetra justo nulla, sed porttitor nunc varius faucibus.',
  ]
]

In version 5.11 the previous example does not work anymore, or neither passing fields as they are saved to block meta (eg using text_left_text_title as key).

Props to @eliaskau for finding this.

Start with includes/acf-value-functions.php around the acf_get_value() field-existence check, then trace how acf_register_block_type() handles example data for group and repeater fields. Confirm the behavior against the provided nested text_left example and saved block-meta keys; done means previews accept the example data without undoing the security fix.