Was there anything in common with the missing emails that would suggest something is flagging them as spam and filtering them out? Could you have crossed some threshold of suspicious words, number of links, etc.? Were they all to the same system, which concluded you were spamming because the mails-per-minute rate shot up?
Usually, if something is rejected as spam, you should get a bounce notice from the receiving email system. Are you somehow filtering those out of your incoming mail? If your server has been flagged as a spam source, you can report this to email@example.com, but without bounce information, LP probably can't do much about it. Getting servers off of spam blacklists generally takes longer than a few hours, so even if someone else had reported the problem, I doubt it would have cleared up that quickly (although anything is possible).
Finally, you weren't sending out a burst of emails that might have triggered a temporary LP shutdown of your account for exceeding an email cap? Last time I checked, it was something like 400 per hour (total incoming and outgoing). I don't recall if there was a per-minute cap, but the number "20" emails per minute sticks in my mind. Anyway, another cause to consider.