boost asio timer hangs the second time I read async - c++

Question

I have a RS485 communication that I talk over with boost::asio::serial_port. I'm testing what happens when there is no connection. The first time the timer cancels the operation. The second time the program just hangs on io.run(). I'm confused, because I create a new fresh timer, reset io and try to have a clean plate before I start to read anything from the wire.
boost::asio::io_context io;
boost::asio::serial_port port;
std::size_t readUntil(std::vector<char>& buffer, char delim, std::chrono::microseconds timeout) {
using boost::system::error_code;
error_code read_result {};
size_t msglen = 0;
io.reset();
boost::asio::system_timer timer(io, timeout);
boost::asio::async_read_until(port, boost::asio::dynamic_buffer(buffer), delim, [&](error_code ec, size_t n) {
timer.cancel();
read_result = ec;
msglen = n;
}
);
timer.async_wait([&](error_code ec) {
if (!ec) {
port.cancel();
throw exception::read_exception(exception::read_exception::Code::TIME_OUT);
}
});
io.run(); // Hangs here, the second time, not the first
if (read_result) {
std::stringstream sstream;
sstream << read_result;
throw exception::read_exception(exception::read_exception::Code::PORT, sstream.str());
}
return msglen;
}
int main() {
//set up port options (baudrate etc)
for(size_t i = 0; i<10; i++) {
std::vector<char> buffer;
readUntil(buffer, '\', std::chrono::microseconds(1000));
}
}