Untraceable Boost.Test framework internal error: unknown reason

I'm using Boost 1.69 when I create a precondition like the following:

struct is_binary_available
        {
            std::string binary_name;

            is_binary_available(std::string&& _binary_name): binary_name(_binary_name) {}

            boost::test_tools::assertion_result operator()(boost::unit_test::test_unit_id)
            {
                return boost::test_tools::assertion_result(!boost::process::search_path(binary_name).empty());
            }
        };

and use it in a certain test case:

BOOST_AUTO_TEST_CASE(FooTest, * (boost::unit_test::timeout(20), boost::unit_test::precondition(sense::test::is_binary_available("python3"))))

the test is failing with the following:

Running 1 test case...
Entering test module "some_test"
../src/myfile.cpp(10): Entering test suite "some_test"
Boost.Test framework internal error: unknown reason

Anyone ever encountered such an error?

Many thanks :)