The DockerSettings.page looks for a running process called dockerd.
<?
// Add the Docker JSON client
require_once "$docroot/plugins/dynamix.docker.manager/include/DockerClient.php";
$DockerClient = new DockerClient();
$DockerStopped = pgrep('dockerd')===false;
function strposX($s, $c, $n=1) {
Not only does it determine if Docker is running on Unraid itself, but it also finds the second Docker daemon running in LXC.
I would suggest checking if the Docker socket is available.
A possible fix would be
$DockerStopped = file_exists("/var/run/docker.sock")===false;