Hi Ben
I'm fairly sure I was the source of this and have replied by email to your response to my 2nd message. The first message I sent, which I assume is the "mystery" one, was sent from my phone and displayed some strange message about 'awaiting moderation' which I had never seen before. This is why I sent the 2nd message from my tablet which obviously has gone through as normal.
I can't see any sign of the original message in my sent items or any other section so I've only added the above detail in case it helps someone with more knowledge of the forum workings to solve the issue.
Brian