Non-responsive navigation menu in web/ESS

We have users intermittently unable to open anything from the left-side navigation menu in either the full web client or in ESS. They can expand any navigation trees, but when clicking on any of the menu options to make it display in the main menu on the right, nothing happens. The user currently having the issue is using Internet Explorer 11, and the cache, cookies, etc have all been cleared. In the past, when users have had this issue, it mysteriously clears up on its own after some time, but I've been tasked with figuring out the cause and finding a real solution other than "try a different browser until it starts working again." Any ideas?