True. In some ways, that's worse. Instead of crashes, you get something working on the wrong data.

I had one bug in a renderer where I'd see object shadows moving across a 3D scene, but not the object casting the shadow. Didn't crash. That was hard to find. A dead index was still in use, and it pointed to something valid enough to be drawn.

Use-after-frees and ABA problems can be addressed by using generation counts with your object pool. Rust's slotmap crate handles this out of the box, AFAIK.