Yeah I’m using Chrome as well, I just tested in Firefox and Safari and it’s still working.
Here’s what I “think” it could be if your client experiences this every once in awhile. I noticed the site sometimes takes a while to load, which would have to do with the hosting/server. My guess is, when the site loads slowly, it takes a while for the javascript files to load which activates the dropdown effect. It’s not always slow, just every once in a while.
Another person had a similar issue here – https://twitter.com/appfinite/status/755792763464056832
Other than that I have no idea what else it could be.