This happened to me and the issue was that the default WIN V3 device codesys puts in the project is the 32 bit Soft PLC.
I had downloaded the x64 codesys IDE and WIN V3 soft PLC, so when I scanned network, it obviously didn't find the device the project had in it.
You can change the device in the project to the 64 bit one by right-clicking on device -> update -> then selected proper one.
The only other thing to check is that you actually have the soft PLC in run; look at your taskbar at lower right on Windows and check if the PLC icon is started, not just up and visible.