People work 60-70 hours each week for really low (I mean LOW) salaries and the ones who are not full-time are interns (probably 65% of company is interns) who are lured in with promises of a position with "social impact" and "purpose" only to be tricked into slaving 40-50 hours and dealing with terrible management, unfulfilling work and more stress than you could imagine.
This experience scarred me and I know it's the same for many others who have left the company. Sexism and degradation runs rampant. There is no understanding of work/life balance and ZERO perks. You are expected to still answer emails and work on weekends, vacation, your son's birthday, while in labor... the list goes on. You forget about the mission of helping children because you never see that component. You could find as much "purpose" working for a corporation that gives to a charity.
My advice to you: ask them about employee turnover. Ask them about Epic's work culture and how many lawsuits they have against them. If they are pressuring you into accepting a low stipend or salary because they "receive hundreds of applications" (not true at all, they are always struggling to keep people and find new ones) so you should take it or leave it, or if you are questioning the interview process, maybe take it as a sign of how the rest of the company is managed.