Merge pull request #4490 from rabbitmq/mk-update-3.9.15-release-notes

Another 3.9.15 release note update

Author: michaelklishin

release-notes/3.9.15.md

@@ -19,6 +19,27 @@ Contributors are encouraged to update them together with their changes. This hel
 
    GitHub issue: [#4371](https://github.com/rabbitmq/rabbitmq-server/pull/4371)
 
+ * When a policy contained keys unsupported by a particular queue
+   type, and later updated or superseded by a higher priority policy,
+   effective optional argument list could become inconsistent (policy
+   would not have the expected effect).
+
+   Kudos to @jaroslaw-bochniak for providing very detailed reproduction steps.
+
+   GitHub issue: [#4463](https://github.com/rabbitmq/rabbitmq-server/pull/4463)
+
+ * Priority queues could run into an exception in some cases.
+
+   Contributed by @luos and @olikasg.
+
+   GitHub issue: [#4405](https://github.com/rabbitmq/rabbitmq-server/issues/4405)
+
+ * Maintenance mode could run into a timeout during queue leadership transfer.
+
+   Contributed by @felixhuettner.
+
+   GitHub issue: [#4468](https://github.com/rabbitmq/rabbitmq-server/pull/4468)
+
 
 ### Prometheus Plugin