I sorted all my notes by size and checked the first few hundred under 500b - at least half have the same icon, and a lot of the titles end with .PDF or .JPG so they were imports from my local folder. That's around 300 notes with missing attachments. The dates range over the past 22 months.
I do have database backups, but don't know when this happened - apart from sometime during the period - so the overhead of finding originals of these notes is probably far worse than managing without them, unless I find something really important missing. (I'm over 9,000 notes and counting now.)
Heather suggested I run the /debugmode database cleanup to try and solve a different issue (an upload count mismatch) so I'll give that a shot and see if anything changes. Meantime and if practical I recommend that you check your database for very small notes of 300b or less and just do a quick check to make sure they have all the content you were expecting...
If the Evernote R&D guys can figure out a viable way to check for corrupted notes it might be a comforting extra for the toolbox too.
Screengrab of the offending note and icon below, or shared version here..