[Mark McLeod]

The other obvious cause would be the video stream is trying to use too much bandwidth and the field drops it.
Images compress differently depending on how complicated the picture is, so if the camera happens to point at an easily compressed picture the bandwidth use can be small, but if the field image is too complicated and it isn't easily compressed then it takes up a lot more bandwidth. I've seen camera bandwidth vary on the field by 2 or 3 Mb/s depending on what the camera was looking at.

As a test for the next time you are on the field, temporarily cut your image stream way down to 320x240 / 10fps / 50% compression. And in the Pit measure your bandwidth using the standard Windows Task Manager->Performance tab.