@Gazumped - " not surprising that a standard viewer dislikes some content", yes you'd be correct if I was expecting to read the Evernote content, but the .enex is XML meaning that first you have the standard XML format, then within that you have evernote specific tags. Its the basic XML format that is broken.
As you also rightly say, the failure of Evernote to import its own exported files is even more of a red flag, any .enex that a current Evernote exports, it should be able to re-import unless there is something else really wrong.
This bug is ironic, because I've been using Evernote since 2010, and many of the company's early team were friends and former colleagues, I was actually doing this export because the large number of Evernote bugs I've been seeing lately make me wonder about its longterm stability. (My offline Evernote is missing a bunch of notes that are on the online one; and the issue with emptying the trash; are just a couple I've hit this week in what used to be a rock steady pair of apps (Desktop and mobile) that I could rely on).