Update known-issues for the features upgrade bug #111014

Author: thecoop

docs/reference/release-notes/8.12.0.asciidoc

@@ -14,6 +14,13 @@ there are deleted documents in the segments, quantiles may fail to build and pre
 
 This issue is fixed in 8.12.1.
 
+* When upgrading clusters from version 8.11.4 or earlier, if your cluster contains non-master-eligible nodes,
+information about the new functionality of these upgraded nodes may not be registered properly with the master node.
+This can lead to some new functionality added since 8.12.0 not being accessible on the upgraded cluster.
+If your cluster is running on ECK 2.12.1 and above, this may cause problems with finalizing the upgrade.
+To resolve this issue, perform a rolling restart on the non-master-eligible nodes once all Elasticsearch nodes
+are upgraded. This issue is fixed in 8.15.0.
+
 [[breaking-8.12.0]]
 [float]
 === Breaking changes

docs/reference/release-notes/8.12.1.asciidoc

@@ -3,6 +3,16 @@
 
 Also see <<breaking-changes-8.12,Breaking changes in 8.12>>.
 
+[[known-issues-8.12.1]]
+[float]
+=== Known issues
+* When upgrading clusters from version 8.11.4 or earlier, if your cluster contains non-master-eligible nodes,
+information about the new functionality of these upgraded nodes may not be registered properly with the master node.
+This can lead to some new functionality added since 8.12.0 not being accessible on the upgraded cluster.
+If your cluster is running on ECK 2.12.1 and above, this may cause problems with finalizing the upgrade.
+To resolve this issue, perform a rolling restart on the non-master-eligible nodes once all Elasticsearch nodes
+are upgraded. This issue is fixed in 8.15.0.
+
 [[bug-8.12.1]]
 [float]
 === Bug fixes

docs/reference/release-notes/8.12.2.asciidoc

@@ -3,6 +3,16 @@
 
 Also see <<breaking-changes-8.12,Breaking changes in 8.12>>.
 
+[[known-issues-8.12.2]]
+[float]
+=== Known issues
+* When upgrading clusters from version 8.11.4 or earlier, if your cluster contains non-master-eligible nodes,
+information about the new functionality of these upgraded nodes may not be registered properly with the master node.
+This can lead to some new functionality added since 8.12.0 not being accessible on the upgraded cluster.
+If your cluster is running on ECK 2.12.1 and above, this may cause problems with finalizing the upgrade.
+To resolve this issue, perform a rolling restart on the non-master-eligible nodes once all Elasticsearch nodes
+are upgraded. This issue is fixed in 8.15.0.
+
 [[bug-8.12.2]]
 [float]
 === Bug fixes