Hey there,
Well first off you add 'after' => '<li class="divider"></li>'
as you can see it will cause problems. Why? I do not know as I did not develop Foundation. That is something you have to ask the Zurbians. It may be because what your adding conflicts with how the top-bar js is written.
So I followed the link above and clicked on https://www.w3schools.com/cssref/sel_last-child.asp
then I opened up the style sheet, played around for about 5 min and came up with the following:
.top-bar-section ul li:last-child {
border-right: solid 1px #4e4e4e;
border-bottom: none;
border-top: none;
}
.top-bar-section ul li li:last-child,
.top-bar-section ul li li li:last-child,
.top-bar-section ul li li li li:last-child
.top-bar-section ul li li li li li:last-child,
.top-bar-section ul li li li li li li:last-child {
border:none
}
This gave me a line or divider on the last menu item. This also added a line on the last menu item in the drop down do I added the extra css to keep this from happening.
All it takes is just a little effort amigo. Hope this helps, and please leave a review of WP-Forge. Enjoy!