On December 17, 2015, Elasticsearch announced the release of versions 2.1.1, 2.0.2, and 1.7.4, which introduced significant bug fixes and improvements. The 2.1.1 version, based on Lucene 5.3.1, addressed critical issues such as translog corruption due to full disk errors, preventing conflicting mappings, and fixing NullPointerExceptions during indexing. It also resolved problems with children aggregation missing documents, tribe node configuration requirements, and performance regression after index deletion. Version 2.0.2 saw some of these fixes backported, while 1.7.4 focused on improving delayed shard allocation for efficient recovery. Users were encouraged to upgrade to these versions, particularly 2.1.1, to benefit from enhanced performance and stability, and to report any issues via GitHub or social media.