How did you come to the conclusion that the speed of the link is changing? I doubt BlueIris has anything to do with it.
Crappy homemade cables are a strong possible cause. You can go into adapter settings in windows and force the link to be a particular speed, but if there's an issue with a cable this will cause problems.
Length of the cable and what is driving the cable in terms of the switch will also have a bearing on the overall connection speed that gets negotiated.