Next and Previous links not working

[Cintia]

The galleries on the website https://dominicschaefer.com/corporate/corp-commercial/ are created with NextGen and I use Slimbox2 for WordPress for the lightbox effect. I know the plugin hasn't been updated in 6 years, but we'd like to stick to this gallery since it's easy to customize the buttons and loading gif.

We like to customize the images for loading, Prev and Next buttons, and it used to work years ago. After the NextGen update, it stopped working.

I went and replaced the CSS and JS files from the official site (this link), pasted them where the plugin files are. The images load correctly, however, the links for the Next and Previous buttons are not working.

I have included a newer version of jQuery in the site header: 

<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>

And have included the CSS code below for reference:

#lbOverlay{position:fixed;z-index:9999;left:0;top:0;width:100%;height:100%;background-color:#000;cursor:pointer;}

#lbCenter,#lbBottomContainer{position:absolute;z-index:9999;overflow:hidden;background-color:#fff;}

.lbLoading{background:#fff url(images/default/loading.gif) no-repeat center;}

#lbImage{position:absolute;left:0;top:0;border:10px solid #fff;background-repeat:no-repeat;}

#lbPrevLink,#lbNextLink{display:block !important;position:absolute;top:0;width:50%;outline:none;}

#lbPrevLink{background:transparent no-repeat 0 15%;left:0;}

#lbPrevLink:hover {background: transparent url(images/default/prevlabel.gif) no-repeat 0 15%;}

#lbNextLink{background:transparent no-repeat 100% 15%;right:0;}

#lbNextLink:hover { background: transparent url(images/default/nextlabel.gif) no-repeat 100% 15%;}

#lbBottom{font-family:Verdana,Arial,Geneva,Helvetica,sans-serif;font-size:10px;color:#666;line-height:1.4em;text-align:left;border:10px solid #fff;border-top-style:none;}

#lbCloseLink{display:block;float:right;width:66px;height:22px;background: transparent url(images/default/closelabel.gif) no-repeat center;margin:5px 0;outline:none;}

#lbCaption,#lbNumber{margin-right:71px;}

#lbCaption{font-weight:bold;}

The JS used hasn't been modified at all.

Any help is appreciated. If you have another lightbox you can suggest that is simple, but can be customized easily in the same way, please let me know.

Thanks!