decltype(auto) return type not deducible in clang

I'm currently fiddling with composed operations in boost asio and can't understand why clang seems unable to deduce the return type of my get_executor() method:

template<class Stream, class Resolver, class CompletionToken>
auto resolve_and_connect(
    std::string_view host,
    std::string_view port,
    Stream& stream,
    Resolver& resolver,
    CompletionToken&& token)
{
    using Signature = void(boost::system::error_code);
    using Handler = BOOST_ASIO_HANDLER_TYPE(CompletionToken, Signature);

    auto initiation = [](auto&& completion_handler, Stream& stream, Resolver& resolver) {
        struct intermediate_handler {
            Handler m_handler;
            Stream& m_stream;

            decltype(auto) get_executor() {
                return net::get_associated_executor(m_handler, m_stream.get_executor());
            }
            // using executor_type = decltype(std::declval<intermediate_handler>().get_executor());
        };

        intermediate_handler{completion_handler, stream};
    };

    return net::async_initiate<CompletionToken, Signature>(
        initiation, token, std::ref(stream), std::ref(resolver)
    );
}

Fails with:

 error: no viable conversion from returned value of type 'typename associated_executor<(lambda at test.cpp:9:71), executor>::type' (aka 'boost::asio::executor') to function return type 'decltype(auto)'
                    return net::get_associated_executor(m_handler, m_stream.get_executor());
                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Compiled with clang version 10.0.0-4ubuntu1 and -std=c++17.

Notice that namespace net = boost::asio; is implicit in the above code.