If you are recording continuous + trigger (the option where is saves substream until motion and then saves mainstream), or only when triggered and are utilizing the substreams, make sure that the pre-trigger time is longer than the iframe interval.
So if you look at camera status in BI, it shows a KEY number. If the number is 1.00, then you need to make the pretrigger at least 1 second or it will be pulling from the substream. I would make it 1.5 to 2 seconds to be safe.
If your KEY is anything but 1.00, then go into the camera gui setting itself (not in BI), and make the FPS and iframes the same. Most of us use 15FPS and 15 iframes.
If your camera doesn't allow you to set iframes, then you need a larger pre-trigger. The smaller the KEY number is, the longer the pre-buffer. 0.25 would be at least 4 seconds as an example.