Gazebo fortress won't load once I add Contact plugin

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I have this sdf file:

<sdf version="1.5">

<world name="rl_world">
    <include>
        <uri>path/to/plane.sdf</uri>
    </include>
    <include>
        <uri>/path/to/robot.urdf</uri>
    </include>
    <plugin filename="libignition-gazebo6-contact-system" name="ignition::gazebo::systems::Contact"> </plugin>
</world>

</sdf>

When I try to load in in gazebo with ign gazebo world.sdf it shows a blank grey screen with no entities. It doesn't give an error to the console. If I remove the plugin line it loads fine. Is there something wrong with it?

plane.sdf has a contact sensor on its only link and the TouchPlugin.