Can't downstrum quickly?

[Ramma2]

Guitar seems to work fine on medium, but when I bump it up to hard and have to play notes in rapid succession, the strum bar can't seem to handle it and I miss notes. I've tried strumming really lighty and I've tried strumming harder than I normally do, it just doesn't register those quick back to back notes. Anyone else have a problem with this?

I pulled out the GH2 guitar and it works fine.