m_xdgConfigPath.filePath(QStringLiteral("/plasma-workspace/shutdown/"))
resolves to /plasma-workspace/shutdown/
Remove the leading slash to make it work properly
Taken from commit 4ce9a4a915511acbd41450da486d8e5d5bae10da in plasma-desktop
The commit history of the KCM can be followed in 9db1c0593e84cdb705fc61cddbdc4e5a9c318b97