This did not help. I am using the W3 total cache plugin, and I just clicked on “Performance -> Purge all Caches”. I reloaded the page in a new private window, the problem remains.
Since you can access the link to a problematic page yourself, you should be able to diagnose the problem on your end – or are you implying that on your computer/browser, the TOC opens just fine? Did you test it?
Also, note that in the backend (in the Post editor window) the TOC does expand just fine. It is only broken in the front-end.