## The problem

Issue langgenius/dify#27291 (closed, 113 comments): ### Self Checks - [x] I have read the [Contributing Guide](https://github.com/langgenius/dify/blob/main/CONTRIBUTING.md) and [Language Policy](https://github.com/langgenius/dify/issues/1542). - [x] This is only for bug report, if you would like to ask a question, please head to [Discussions](https://github.com/langgenius/dify/discussions/categories/general). - [x] I have searched for existing issues [search for existing issues](https://github.com/langgenius/dify/issues), including closed ones. - [x] I confirm that I am using English to submit this report, otherwise it will be closed. - [x] 【中文

## The verified fix

Contributor DhruvGorasiya identified the root cause: Weaviate 1.27.0+ requires the new named-vectors schema format (vectorConfig); existing knowledge data stored by Weaviate 1.19.0 uses the old format, so queries with weaviate-client v4 fail. The team published a migration guide and migration scripts preserving embeddings (see docs/weaviate/WEAVIATE_MIGRATION_GUIDE). Reporter-confirmed workaround from xiaoyesoso: change the knowledge base's embedding model, which triggers an automatic index rebuild and restores the knowledge base.