First… try to refresh your app to reconnect. If this does not work make sure that the entry point in your application is actually creating an instance of Overmind. The code createOvermind(config) has to run to instantiate the devtools.
This is also a common misconception about the ports. You want
createOvermind to connect to the port defined inside the Devtool, which is
3031 by default.
Restart VS Code
Operators are identified with a Symbol. If you happen to use Overmind across packages you might be running two versions of Overmind. The same goes for core package and view package installed out of version sync. Make sure you are only running on package of Overmind by looking into your node_modules folder.