Click on Span Object not working occasionally

I have the following menus in my application 

When I click on 'Self Service Tool' menu or hover over it, the following submenus displays

Here is my code to click on the 'Self Service Tool' submenu.

var Wait = require("Wait");
var browser = Sys.Browser();
var page = browser.Page("*");
Wait.findObject("//li/a/span[contains(text(),'Self Service Tool')]").Click();
Delay(1000);
Wait.findObject("//li/a/span[contains(text(),'Prior Authorization Work Queue')]").Click();
Delay(3000);

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function findObject(selector)
{
var browser = Sys.Browser();
var page = browser.Page("*");
var obj = page.WaitElement(selector,1000);
while (obj.Exists == false){
obj = page.WaitElement(selector,1000);
}
return obj;
}

 The click on the 'Self Service Tool' object occasionally not working. The HTML attributes of the object are shown below.

In the logs, I can see Click is performed but the sub-menu list is not populating