When I'm playing the CS80v from a MIDI keyboard some patches produce no sound but the keys on the CS80v still go up and down as I press the keys on my keyboard.
On the CS-80V, there's also a midi channel parsing in the multi mode.
When using a multi preset, you can choose a particular midi channel for each of the 4 zones defined in the right part of the multi page.
Some of the factory presets may have some zones not configured on omni. In that case, the virtual keyboard is playing, but if your keyboard is not on the midi channel corresponding to the zone, it won't play anything.
Just select 'omni' as the midi channel of the zone, and it should fix your problem.