ui.bootstrap modal does not load modal content, it only shows backdrop

Question

The issue is for the fist time only other times it works fine. When i tried to open modal as below.Some times the modal content which tied to templateUrl is not rendered, it only shows backdrop with out modal content.I am using angular-ui-bootstrap version Version: 2.4.0. Kindly help me in finding the issue. The issue is rarely reproduced not all the times.

dialog = $uibModal.open({
            animation: true,
            scope: scope,
            size: "lg",
            backdrop: 'static',
            keyboard: false,
            templateUrl: 'question.html',
            windowClass: 'ep-std-dialog-position'
        });