Go to LW's menu bar, View menu -> Show Hide Connections. Then right-click heading bar & tick option to show vendor/version. Now take a careful look at the ultrapeers you are connected to. If you see one that is not LW version 4.18, then select it & press Remove button. Wait ... you may partially lose connection a little. Wait until LW settles & finds a new ultrapeer. Then try your search again.