This is highly sector dependent. I've worked at startups for almost my entire career and a big peak of leaving engineers at 2-3 years wouldn't even cause me any

This is highly sector dependent. I've worked at startups for almost my entire career and a big peak of leaving engineers at 2-3 years wouldn't even cause me any concern. In the 10 years in industry I've worked I'd argue the average engineer leaves around the 5 year mark. This typically coincides with a failed seed round or reaching a terminal title (senior, staff, etc) and not being able to go further. The fresh grads case is a good point. The one company I left fairly quickly was almost entirely powered by intern/junior labor. Seniors left quickly due to a combination of bad management, low advancement opportunities, and constantly having to re-train people. This, I think, is worth looking out for.