Symfony yaml parser not working

Hello,

I have problems with spyc in my CMS which uses its own autoloader.
That’s why I wanted to switch to the Symfony Yaml Parser.

I installed device detector via composer and deleted the mustangostang/spyc folder in /vendor.
I then tried to switch to Symfony like this:

use DeviceDetector\ClientHints;
use DeviceDetector\DeviceDetector;
use DeviceDetector\Yaml\Symfony as DeviceDetectorSymfonyYamlParser;

...

$this->DeviceDetector = new DeviceDetector($this->userAgent, $clientHints);
$this->DeviceDetector->setYamlParser(new DeviceDetectorSymfonyYamlParser());
echo $this->DeviceDetector->getYamlParser()) # prints DeviceDetector\Yaml\Symfony
echo 'A'; # is printed
$this->DeviceDetector->parse();
echo 'B'; # is NOT printed

Instead a Class 'Spyc' not found error is thrown.
Any ideas what might be wrong with this approach?

Thanks and kind regards