Hello @oli.hod. It seems to be working as expected. The Stereo switch will basically make the Plug-In act like two separate instances, and if you leave it at mono by default, it will take both tracks as a single signal since the switch indicates the input mode.
The other option would be to insert an instance of the Plug-In on each track/side. If you’re experiencing performance issues, please take a look at our optimization guides for PC and macOS.