Sounds like what you are describing is normal behavior. Event videos record 12-second videos with a 5-minute cool down period. So if 1 person exits and you get a video it will not catch the second person unless they exit 5-minutes after the first. This is done to save on server costs since they offer it free.
You can do event recording to an SD card and it will record all events without any cool down period but you would not get notifications for SD card events.
They are also testing a pay version that would reduce or eliminate the cool down and extend the videos to catch all the motion instead of 12 seconds. More information on that can be found in this thread: