Show HN: Gmail bug blocking email with subject containing "ll" and then "c"

I have been experiencing a very odd bug with Gmail today, it seems that if you send an email to an @gmail address with the string "ll" flowed at some point later by a "c" in the subject (e.g. "you will recognise this") the email will never arrive. It doesn't happen with apps accounts and I have tested it with about 6 different peoples Gmail accounts and multiple sending servers and addresses. It very odd! I have reported it to Google - although when I thought it was just the string "will recognise". Does anyone have any idea what could be causing it?