“We have identified a bug in some versions of Evernote for Mac that can cause images and other attachments to be deleted from a note under specific conditions. We believe you are one of a small number of people impacted by this bug.” The good news is that according to Evernote, only a small number of users have been affected by the bug, so if your files are still intact then we guess you’re safe, although you should probably still update anyway lest you do something that could trigger the bug and lead to the loss of all your attachments.
Even better news is that Evernote has tried to restore all the lost attachments and for the most part were successful, although it wasn’t a 100% win. Alternatively users will be able to try and restore the files themselves via the note history feature which is only available to Premium users, which is a service that Evernote will be providing to affected users for free for an entire year.