How to call 2 different symfony voters

I have a symfony voter in a bundle that lives in the vendor folder. it works as expected:

class PlaylistVoter extends Voter
{

public function __construct()
    {}

    protected function supports($attribute, $subject)
    {}

    protected function voteOnAttribute($attribute, $subject, TokenInterface $token)
    {
      if(<someclause>) {
          return true;
      }

      return false;
    }

}

I am now configuring another voter, but this is in the symfony core (/src/mybundle). It is pretty much the same as the previous one, only the content of the voteOnAttribute method changes.

Using breakpoints, I can see the voteOnAttribute method in the voter in vendor gets called as expected, but the one in the voter in the core never gets called.

using debug:container, I can see they are both correctly configured. Also I can see the constructor gets called, but voteOnAttribute gets not.

thanks for any suggestion.