I’ve not used the WT3 cache plugin so off hand I do not know what kind of features or settings it has to offer. But this is just like I said about my own site that uses Joomla. I use a plugin for doing similar things but sometimes when minifying css or scripts, it could affect how something in the site works. Because this relates to a third party plugin, my best suggestion is to contact their support and let them know that the WT3 cache is conflicting with the mobile menu which uses a combination of css and a script.
My question though is what are you minifying….css or scripts?