CHANGELOG updates

CHANGELOG.md

@@ -3,17 +3,19 @@
 librdkafka v2.3.1 is a maintenance release:
 
  * Fix hang in cooperative consumer mode if an assignment is processed
-   while closing the consumer (#).
+   while closing the consumer (#4528).
 
 
 ## Fixes
 
 ### Consumer fixes
 
- * While using the cooperative assignor, given an assignment is received while closing the consumer
+ * Issues: #4527.
+   While using the cooperative assignor, given an assignment is received while closing the consumer
    it's possible that it gets stuck in state WAIT_ASSIGN_CALL, while the method is converted to
    a full unassign. Solved by changing state from WAIT_ASSIGN_CALL to WAIT_UNASSIGN_CALL
-   while doing this conversion (#).
+   while doing this conversion.
+   Happening since 1.x (#4528).