@yit I could think of these possible reasons.

1. Autocomplete relies on metadata to provide suggestions. Ensure the workspace is enabled for Unity Catalog and that the user has the necessary permissions to access the metadata for the tables containing the nested JSON data.

2. Autocomplete might not yet fully support the intricacies of nested JSON path expressions and schema inference. This might be an area of ongoing development or a known issue being addressed by Databricks. You can email databricks support for it.

3. Consider defining the schema for your JSON data, especially for nested structures, as it may help with autocomplete accuracy instead of using infer schema.