We were recently made aware of a bug that was a part of the recent PDF changes we've made. When you sent a letter template as a PDF attachment within Cliniko, it wouldn't actually send the email due to a hidden error. Not only have we just made a change that fixed this error, but also correctly sent off any emails that were held up as a result of the bug.
If this had affected any of your emails at all, there's nothing you'll need to do. But sorry about the bug everyone!