There is a bug in the SA code introduced by JDK-8061802.
This patch seems to fix the issue:

--- a/agent/src/share/classes/sun/jvm/hotspot/memory/GenCollectedHeap.java
+++ b/agent/src/share/classes/sun/jvm/hotspot/memory/GenCollectedHeap.java
@@ -76,9 +76,9 @@
 
     switch (i) {
     case 0:
- return genFactory.newObject(youngGenField.getAddress());
+ return genFactory.newObject(youngGenField.getValue(addr));
     case 1:
- return genFactory.newObject(oldGenField.getAddress());
+ return genFactory.newObject(oldGenField.getValue(addr));
     default:
       // no generation for i, and assertions disabled.
       return null;