From: https://markets.businessinsider.com/currencies/news/tron-ceo...

Looks like he complained about some health issues:

"[Justin Sun] unexpectedly dropped out days before the scheduled lunch date, blaming a bout of kidney stones. However, he apologized on social media for overpromoting himself, and Bloomberg reported that Chinese authorities briefly detained Tron employees, sparking conspiracies that he bowed out under pressure from Beijing."