So first I clicked on Potluck mode, ran and failed multiple times. Each time after I failed, I would simply head right back to the Custom Night and without touching anything at all. I'd simply hit Play. Since the game mode saves any settings that were set prior to starting the previous Custom Night. Was I supposed to be going and clicking the Potluck option every single time?
Viewing post in Bug Report Thread
To update on my side of things, I can now confirm that I started up the game fresh; went into Custom Night mode, selected Potluck, and clicked nothing else besides Play to start it up. Completed it on the first try of that session and still got no third star, so there definitely seems to be something tied to the star unlock trigger.