Since the last update of the Twitter iOS app a week ago (version 8.52.1), the Evernote button has disappeared from the share menu and there doesn't appear to be any way of adding it back. On the latest version of the iPad OS Twitter app, it's still possible to share with Evernote.
I realise this may be out of Evernote's hands but is there a change in policy that has resulted in this? It's frustrating, as the Twitter integration had been greatly improved recently, with adding tags made a lot easier.