Boost log not showing named scope in shared object code

I'm using boost log (v1.71) to try and write logs. Our architecture involves a set of dynamically loaded shared objects, and I'm having trouble using the named scope attribute in the shared objects.

I am setting up a global logger in one of our support util libraries, which has logger.hh and logger.cxx:

//logger.hh

#include <boost/log/trivial.hpp>
// etc.

BOOST_LOG_GLOBAL_LOGGER(my_logger, src::severity_logger_mt<trivial::severity_level>)

#define LOG_TRACE BOOST_LOG_SEV(my_logger::get(), trace)
// etc...

and

//logger.cxx

BOOST_LOG_GLOBAL_LOGGER_INIT(my_logger, src::severity_logger_mt<trivial::severity_level>)
{
  src::severity_logger_mt<trivial::severity_level> lg;
  lg.add_attribute("Scope", boost::log::attributes::named_scope());
  return lg;
}

These get built into a shared library, linked at compile time to the main application and the dynamically loaded plugins. In the main application I'm initialising the logger:

//main.cxx
#include "logger.hh"

int main()
{
  logging::formatter fmt = expr::stream
     << expr::format_named_scope("Scope", keywords::format = "%n") << " - " << expr::message;

  logging::add_console_log(std::clog, keywords::format = fmt);

  BOOST_LOG_NAMED_SCOPE("main");
  LOG_WARNING << "test log";

  // Main code continues, including dynamically loading plugin shared objects.
}

Finally in the shared object plugin, linked to the util library:

//plugin.cxx

void Activity()
{
  BOOST_LOG_NAMED_SCOPE("Activity");
  LOG_WARNING << "activity log";
}

I have heavily paraphrased a lot of this, but hopefully all the key ingredients are here. Currently the output for running the program looks like:

main - test log
 - activity log

Can anyone help me understand what I need to do to get the named scopes working? I appreciate that the use case here is unusual, but I would prefer to keep the single global logger shared between the whole program.

Using gcc 4.8.3, on RHEL7.