Nicesroll not showing at page with dynamic height

Here if you click on the arrow – text appears and there should be nicesroll sroller, but it doesn’t seem to appear. How to fix it? if it’s not dynamic it works, but that way not.

jquery code here:

function() {
$("article").niceScroll({cursorcolor:"#fff",autohidemode:false, zindex: 999});
$("#nicesroll").click(function() {

CSS is

article {
padding: 15px;
max-height: 400px;
overflow-y: auto;

Thanks for advice