Demos can be troublesome at times. It's the nature of it so be cool about it:
Just say 'hold a sec', open the console and see what's there.
Do not forget that how you remedy/react under stressful conditions is also an important asset that can increase your credibility even more than the demo itself in the eyes of your viewers.
If the code is not working, the team must be called for support. All the options of the code and paper writer free are halted for the students. Such fieldwork is improved for the working of the code on all devices.