OpenBiome Project Manager interview questions

I applied online then had a phone interview a week later with HR. I was offered an in person interview with 4 people. Saturday afternoon (2 days before the actual interview), I was sent a 30 minute presentation exercise. I initially thought that it was very inconsiderate to send that last minute but maybe it was to test how I would handle pressure? The in person interviews were decent. I was offered the position the next day. Salary negotiated, offer letter signed, start date confirmed, and my resignation letter submitted. One week before my start date, I emailed for follow-up and was told that they can no longer hire me. They had their reasons but I find it very insensitive. A non-profit that lacks leadership and integrity is not a good one, despite the mission/research.