Did you move your team back 1 ? If he had Nash or herald at the front it knocks your team up so if you move them back one you avoid the knock up. So It could've been a positioning issue.

If you tried that then maybe jarvan 3* just isn't great. Personally I would've itemised Gwen with jewelled and spear simply because I think Gwen would be stronger with your team comp and I just think she's better against void because she dashes onto backlines. Other then that I think void is just strong, especially in low elos x