Elastic Cloud outage on 2026-08-14: Elasticsearch 9.5.1: false-positive matches in certain boolean queries

Elasticsearch 9.5.1 contains a known issue where boolean queries containing a must, filter, or should clause using a multi-value terms query, alongside a must_not clause on fields with disabled indexing, can still return false-positive matches. While the patch in 9.5.1 (https://github.com/elastic/elasticsearch/pull/155936) resolved the bulk-scorer defect for term and range query paths; multi-value terms queries utilize a different Lucene query type that was not covered by that fix. Time Series Data Streams (TSDB) and columnar indices/data streams remain affected for this query pattern, as indexing is disabled by default on those fields. Affected terms queries may return false-positive matches (including documents that should have been excluded) and report higher document counts than expected. No error is raised, so queries will appear to complete successfully. What you can do: - If you have not yet upgraded to 9.5.*, we recommend deferring the upgrade until version 9.5.2 is available. - If you are already running 9.5.*, contact Elastic Support if you need help determining whether your searches are affected. We have identified the root cause, a fix is in progress, and we are preparing a patch release. We will provide a further update when the fix is ready.