When running a Browbeat+Rally use case which does:
Create a network
Create a sbunet
Create a router
Attach router to subnet and oublic network
Boot VM with floating IP
Ping VM

with concurrency 8 and times set to 50 we see that some VMs remain unpingable even after 300 seconds and we see a lot of the following exceptions in karaf logs

2017-09-01 12:19:16,060 | ERROR | eChangeHandler-5 | AsyncDataTreeChangeListenerBase | 319 - org.opendaylight.genius.mdsalutil-api - 0.2.2.Carbon | Thread terminated due to uncaught exception: AsyncDataTreeChangeListenerBase-DataTreeChangeHandler-5
java.lang.NullPointerException
at org.opendaylight.netvirt.vpnmanager.VpnUtil.getIsExternal(VpnUtil.java:1695)[360:org.opendaylight.netvirt.vpnmanager-impl:0.4.2.Carbon]
at org.opendaylight.netvirt.vpnmanager.SubnetmapChangeListener.update(SubnetmapChangeListener.java:107)[360:org.opendaylight.netvirt.vpnmanager-impl:0.4.2.Carbon]
at org.opendaylight.netvirt.vpnmanager.SubnetmapChangeListener.update(SubnetmapChangeListener.java:29)[360:org.opendaylight.netvirt.vpnmanager-impl:0.4.2.Carbon]
at org.opendaylight.genius.datastoreutils.AsyncDataTreeChangeListenerBase$DataTreeChangeHandler.run(AsyncDataTreeChangeListenerBase.java:160)[319:org.opendaylight.genius.mdsalutil-api:0.2.2.Carbon]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)[:1.8.0_141]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)[:1.8.0_141]
at java.lang.Thread.run(Thread.java:748)[:1.8.0_141]