Hi Monica,
This is an issue I’ve been working on. I’m currently writing the next release of PennController. It’s still a beta, but hopefully it should be stable enough to run your experiment. I’ve uploaded it to a copy of your project and the preloading seemed much improved:
https://github.com/PennController/penncontroller/blob/master/dist/PennController.js
Let me know if you still experience issues
Jeremy