WebLogic JNDIServiceLocator

Today there was a JNDI lookup failing across 2 clusters hosted on same machine but different NIC:

WLS_FW.JNDIServiceLocator BEA-000000
Error loading /somepath from 111.222.123.123:6481
java.lang.NullPointerException
 at weblogic.utils.io.ChunkedDataOutputStream.writeUTFChars(ChunkedDataOutputStream.java:181)
 at weblogic.utils.io.ChunkedDataOutputStream.writeUTF(ChunkedDataOutputStream.java:141)
 at weblogic.workarea.StringWorkContext.writeContext(StringWorkContext.java:32)
 at weblogic.rjvm.MsgAbbrevOutputStream.writeContext(MsgAbbrevOutputStream.java:124)
 at weblogic.rjvm.MsgAbbrevOutputStream$NestedObjectOutputStream.writeContext(MsgAbbrevOutputStream.java:751)
 at weblogic.workarea.spi.WorkContextEntryImpl.write(WorkContextEntryImpl.java:85)
 at weblogic.workarea.WorkContextLocalMap.sendRequest(WorkContextLocalMap.java:150)
 at weblogic.rmi.provider.WorkServiceContext.writeExternal(WorkServiceContext.java:56)
 at java.io.ObjectOutputStream.writeExternalData(ObjectOutputStream.java:1458)
 at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1429)
 at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1177)
 at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:347)
 at weblogic.rjvm.MsgAbbrevOutputStream.writeObject(MsgAbbrevOutputStream.java:627)
 at weblogic.rjvm.MsgAbbrevOutputStream.marshalUserCustomCallData(MsgAbbrevOutputStream.java:357)
 at weblogic.rjvm.BasicOutboundRequest.transferThreadLocalContext(BasicOutboundRequest.java:126)
 at weblogic.rmi.internal.BasicRemoteRef.getOutboundRequest(BasicRemoteRef.java:204)
 at weblogic.rmi.cluster.ClusterableRemoteRef.invoke(ClusterableRemoteRef.java:465)
 at weblogic.rmi.cluster.ClusterableRemoteRef.invoke(ClusterableRemoteRef.java:285)
 at weblogic.jndi.internal.ServerNamingNode_12130_WLStub.lookup(Unknown Source)
 at weblogic.jndi.internal.WLContextImpl.lookup(WLContextImpl.java:440)
 at weblogic.jndi.internal.WLContextImpl.lookup(WLContextImpl.java:426)

The issue is still under investigation... these flags might help:

-Dweblogic.kernel.debug=true
-Dweblogic.debug.DebugConnection=true 
-Dweblogic.StdoutDebugEnabled=true 
-Dweblogic.log.LogSeverity=Debug 
-Dweblogic.log.LoggerSeverity=Debug

I could not find documentation of how internally WebLogic implements the RJVM communication protocol...