Update 2.16.19 release notes

Change-Id: Icccb2c3dcac8529a3480fa6083bae1557d1fed44
diff --git a/pages/site/releases/2.16.md b/pages/site/releases/2.16.md
index 7131b82..e76bcf5 100644
--- a/pages/site/releases/2.16.md
+++ b/pages/site/releases/2.16.md
@@ -637,6 +637,11 @@
     This helps to speedup online migration at the expense of imposing a
     higher load on the Gerrit server running at the same time.
 
+  * Add a new metric for monitoring Java deadlocks.
+
+    The metric `proc/jvm/thread/num_deadlocked_threads` monitors the number of
+    threads that are deadlocked waiting for object monitors or ownable synchronizers.
+
   * Add support for Elasticsearch 7.7.
 
 * End-to-end Tests Improvements
@@ -693,6 +698,12 @@
     It was possible to remove the email address associated with the primary
     id of a Realm, effectively resulting in the account being removed.
 
+  * [Isssue 12786](https://bugs.chromium.org/p/gerrit/issues/detail?id=12786):
+  Fix wrong status returned when auth backend couldn't be reached.
+
+    The response 401 was returned when the auth backend could not be
+    reached, instead of the response 503.
+
   * Fix internal server error on parsing commit message during receive commits.
 
   * Add `autocomplete="off"` to LDAP login form.