Add changelog entry

Signed-off-by: Andrew Ross <andrross@amazon.com>

Author: andrross

CHANGELOG.md

@@ -63,6 +63,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Null check field names in QueryStringQueryBuilder ([#18194](https://github.com/opensearch-project/OpenSearch/pull/18194))
 - Avoid NPE if on SnapshotInfo if 'shallow' boolean not present ([#18187](https://github.com/opensearch-project/OpenSearch/issues/18187))
 - Fix 'system call filter not installed' caused when network.host: 0.0.0.0 ([#18309](https://github.com/opensearch-project/OpenSearch/pull/18309))
+- Fix MatrixStatsAggregator reuse when mode parameter changes ([#18242](https://github.com/opensearch-project/OpenSearch/issues/18242))
 
 ### Security