grpc builder.BuildAndStart() hangs on aarch64 but not x86_64 - c++

Question

I have the grpc route_guide example working on both aarch64 and x86_64 but when I translate this example into an already existing (CMake) project only x86_64 works. The aarch64 just hangs in server.BuildAndStart()
The code is identical for the 2 platforms:
void RunServer(const std::string& db_path) {
std::cout << "RunServer" << std::endl;
std::string server_address("0.0.0.0:50051");
RouteGuideImpl service(db_path);
ServerBuilder builder;
builder.AddListeningPort(server_address, grpc::InsecureServerCredentials());
builder.RegisterService(&service);
//builder.SetSyncServerOption(ServerBuilder::SyncServerOption::MAX_POLLERS,2); // Doesn't make a difference
std::cout << "Before builder.BuildAndStart()" << std::endl;
std::unique_ptr<grpc::Server> server(builder.BuildAndStart());
std::cout << "After builder.BuildAndStart()" << std::endl;
std::cout << "Server listening on " << server_address << std::endl;
server->Wait();
}
Using gdb I can see that x86_64 starts 1+4 threads and then listens for grpc traffic. It also works using any other example for route guide (e.g both in C++ and node) communicating with this.
(gdb) run
Starting program: /home/me/mycode/grpc_project/build/myexecutable
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
[New Thread 0x7fffd0bd9700 (LWP 30537)]
RunServer
DB parsed, loaded 100 features.
Before builder.BuildAndStart()
[New Thread 0x7fffd03d8700 (LWP 30538)]
[New Thread 0x7fffcfbd7700 (LWP 30539)]
[New Thread 0x7fffcf3d6700 (LWP 30540)]
[New Thread 0x7fffcebd5700 (LWP 30541)]
After builder.BuildAndStart()
Server listening on 0.0.0.0:50051
But on the aarch64 platform only 1+2 threads are started then grpc hangs
Starting program: /home/ubuntu/mycode/grpc_project/build/myexecutable
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/aarch64-linux-gnu/libthread_db.so.1".
[New Thread 0x7fab553030 (LWP 27568)]
RunServer
DB parsed, loaded 100 features.
Before builder.BuildAndStart()
[New Thread 0x7faad53030 (LWP 27569)]
[New Thread 0x7faa553030 (LWP 27570)]
Where to start debugging this and what could the root cause be?
Others (both here at SO and elsewhere) have suggested limiting the number of threads using ResourceQuota like this
grpc::ResourceQuota rq;
rq.SetMaxThreads(n); // n=1 or n=2
builder.SetResourceQuota(rq);
But it makes no difference, aarch64 still hangs
Ubuntu 16.04 with aarch64 (Nvidia TX2)