I try to isolate the problem in a small and simple reproducer by extracting the data from my real setup.
I fails with NPE at :
It fails only with the Thread.sleep. If you uncomment it, it won't fail.
So, you may have to increase the sleep time depending of your environment.
I know this is not a very rigourous test, but this is the only way I've found to reproduce it.
You can find the reproducer here :