Recently, I noticed that, as long as I am a logged in user, a Wikidata page would not display a HTML link for the Enzyme commission number (P591). I tried that on Firefox (49.0) and Chrome (54.0) (I think this also applies to older versions) on Linux. When I log out of an account or use an anonymous session, the HTML link is being displayed as expected. I recall that I had this issues on other properties as well, but it could usually be fixed with one to several page reloads. This does not work here.
Thanks and cheers,