In Elasticsearch 5.3.0, a bug affecting users who configure a custom data path could lead to data loss if not managed correctly. The issue arises when the `path.data` setting in the `elasticsearch.yml` file is specified as an array, causing it to merge with the `default.path.data` setting instead of replacing it. This can result in multiple data paths being used, potentially leading to shard allocation in unexpected locations and startup failures for additional nodes due to path locking conflicts. To mitigate the bug, users should adjust their configuration to use a comma-separated string for `path.data`, ensuring it overwrites `default.path.data`. Additionally, data from the default path must be moved to the other specified paths before restarting nodes, with the process verified through cluster health checks. Future versions, starting from Elasticsearch 5.3.1, will include a fix for this issue and will prevent the node from starting if shard data is found in the `default.path.data` directory, prompting users to clear or relocate the data to avoid complications.