XHProf/XHGui Importing Profiles

Question

The external/import.php script seems to not work for me. I am using the Docker installation as well as the local webapp. I tried to use an Json-File I created by profiling my Symfony-Webapp and encoding the XHProf output to Json. The Json-File looked like this:

    {
    "Composer\\Autoload\\ClassLoader::loadClass==>Composer\\Autoload\\ClassLoader::findFile": {
      "ct": 5,
      "wt": 22,
      "cpu": 0
    },
    "Composer\\Autoload\\includeFile==>load::dotenv\/Dotenv.php": {
      "ct": 1,
      "wt": 1120,
      "cpu": 0
    },
    "Composer\\Autoload\\ClassLoader::loadClass==>Composer\\Autoload\\includeFile": {
      "ct": 5,
      "wt": 5143,
      "cpu": 0
    },
    "spl_autoload_call==>Composer\\Autoload\\ClassLoader::loadClass": {
      "ct": 5,
      "wt": 5293,
      "cpu": 0
    },
    "main()==>spl_autoload_call": {
      "ct": 4,
      "wt": 39240,
      "cpu": 31250
    },
    "main()==>Symfony\\Component\\Dotenv\\Dotenv::__construct": {
      "ct": 1,
      "wt": 5,
      "cpu": 0
    },
    "main()==>dirname": {
      "ct": 1,
      "wt": 4,
      "cpu": 0
    },
    "Symfony\\Component\\Dotenv\\Dotenv::bootEnv==>is_file": {
      "ct": 1,
      "wt": 74,
      "cpu": 0
    },
    {...},

The File itself has about 6.000 Lines. While I am trying to import it using the script, nothing really happens. After about an hour I aborted the process and retried it with a Json File containing about 20 Lines. I then executed the command again. This time, it ended the process after about 5 minutes, but there were no changes in the database, nor in the webinterface.

After searching a whole day for any documentations my only results seemed to be outdated, since they included the external/headers.php file, which is no where to be found in the current master. Has anybody an idea how to import these profiles than? Had I missed some Data I should have included?