updated known issues

Author: l-trotta

docs/release-notes/known-issues.md

@@ -7,6 +7,10 @@ navigation_title: "Known issues"
 
 For detailed issues, refer to the [Java client repo](https://github.com/elastic/elasticsearch-java/issues).
 
+## 9.x [known-issues-9-x]
+
+All 9.x versions of the client previous to, respectively, 9.2.4, 9.1.10 and 9.0.9 are affected by a bug with the new Rest5Client where memory usage is substantially higher than necessary.
+This problem was [fixed](https://github.com/elastic/elasticsearch-java/pull/1122) in 9.2.4, 9.1.10 and 9.0.9.
 
 ## 9.0.0 [known-issues-9-0-0]
 
@@ -55,4 +59,4 @@ implementation("org.elasticsearch.client:elasticsearch-rest-client:8.16.6")
     <artifactId>elasticsearch-rest-client</artifactId>
     <version>8.16.6</version>
 </dependency>
-```
+```