All of the motors slow down and become less powerful when plugged int the arena itself

When we were competing the other day our robot’s motors all went down to about 20% when they were plugged into the arena. When we used the same competition program on our own with a testing box everything worked fine. I have though about the temperatures of the motors, especially the flywheel, but this problem only occurs inside the arena. Any ideas?

What comes to mind to me is how you use the competition template. You run a preauton when plugged into the arena, so if the preauton contains some commands that limit the velocity, it could affect only when allowed the preauton state.