Apple's iMessage implementation loses messages all the time. It happens about once every month between my girlfriend and I.

I have also had iMesages be sent to the wrong recipient. In one ongoing case, my aunt and uncle frequently receive each other's iMessages, suggesting it's related to their group carrier plan but it's hard to say. The extended family all knows to use SMS instead, which reliably goes to the intended recipient. They are both retired and always together so they haven't reached the point of getting a new plan.