Why is jQuery 'each' function only returning the first element?

You can't have two items with the same id in html. If you want to match both div items, then you would need something like this.

$('[id*="pcnt"]').each(function(){
   // Do your stuff...
});

<div id="match1">
    <div id="pcnt1" name="1">
    </div>
</div>
 
<div id="match2">
    <div id="pcnt2" name="2">
    </div>
</div>

I can say what I can see from your code. The problem is not the method .each which of course should traverse the full set of elements, but the set of element itself, more exactly, the selector you use.

Your selector is the "id selector", based on the attribute id. The purpose of this attribute is the unique identification of some element. So, the selector should not make a set of more then one element, by definition. Now, your HTML actually contains more then one case of id="pcnt". In other words, this is not a valid HTML. I don't know how JavaScript is supposed to act on invalid HTML and I don't know if it is ever prescribed by the ECMAScript standard. You should rather be on the safe side and assume that JavaScript can give you unpredictable results. In other way, you should always provide valid HTML.

I hope you got the point. Now, what to do in your case? How to traverse all the div elements you want? It's really up to you, but you certainly need to use some other selector. For example, they can have some common CSS class applied only to these DIVs; or you can have only these DIVs on the whole page. Look at the available selectors to see the possibilities you can use:
http://api.jquery.com/category/selectors/[^].

See also:
http://api.jquery.com/jQuery.each/[^],
http://api.jquery.com/id-selector/[^],
http://en.wikipedia.org/wiki/ECMAScript[^].

—SA

It happens because the elements have the same ID, when you select an element using $("#id") jQuery uses document.getElementById to retrive it back, but this function returns just one element(the first with the given id).
so, if you want to apply something to multiple elements i think you should use css classes selector $(".class"). And you should not give the same ID to multiple elements.

something like

<div>
    <div class="element">
    </div>
</div>
 
<div>
    <div class="element">
    </div>
</div>

and your script

$(".element").css('opacity', '0');