Just wanted to share this quick tip I heard from a VEX veteran with all of the teams around the world entering really large events. So the VEX Net keys have 250 different wireless channels. Of those, 150 channels are reserved for field control systems like the control switch. This means that only 100 channels are open to wireless. So... if you plug in your controller before turning it on, you will have access to those reserved channels. However, if you turn the controller on before plugging it in, you will be on the same channels as everybody else, not playing in your match. This means you if you lose connection, you may not be able to regain it as someone may have taken the channel you were using.
Every year this problem comes up at my state tournament and the more people that know how to fix it the better. Let me know if my understanding is wrong in any way.