I have set up a portfolio using NextGEN Galleryview, which was working just fine until I installed Autoptimize. With Autoptimize activated, the previous and next arrows in Galleryview disappeared. Specifically, using Firebug I was able to discern that the path was now src="undefineddark/next.png". The arrows reappeared once I deactivated Autoptimize.
Using Autoptimize got me from an F to an A on YSlow...would love to use it or something equivalent if it won't break my gallery.