grpc: java-csharp interop failed with INTERNAL: Connection closed with unknown cause

https://grpc-testing.appspot.com/job/gRPC_interop_pull_requests/11469/testReport/junit/(root)/tests/cloud_to_cloud_java_csharpcoreclr_server_custom_metadata/

Feb 17, 2017 7:48:10 AM io.netty.util.internal.MacAddressUtil defaultMachineId
WARNING: Failed to find a usable hardware address from the network interfaces; using random bytes: 05:48:18:20:6f:30:58:f0
Exception in thread "main" io.grpc.StatusRuntimeException: INTERNAL: Connection closed with unknown cause
	at io.grpc.stub.ClientCalls.toStatusRuntimeException(ClientCalls.java:227)
	at io.grpc.stub.ClientCalls.getUnchecked(ClientCalls.java:208)
	at io.grpc.stub.ClientCalls.blockingUnaryCall(ClientCalls.java:141)
	at io.grpc.testing.integration.TestServiceGrpc$TestServiceBlockingStub.unaryCall(TestServiceGrpc.java:408)
	at io.grpc.testing.integration.AbstractInteropTest.customMetadata(AbstractInteropTest.java:962)
	at io.grpc.testing.integration.TestServiceClient.runTest(TestServiceClient.java:264)
	at io.grpc.testing.integration.TestServiceClient.run(TestServiceClient.java:197)
	at io.grpc.testing.integration.TestServiceClient.main(TestServiceClient.java:81)
Shutting down

Maybe a java issue? @ejona86