Inside the Apple M1 is an incredibly quirky GPU - TechSpot

Obviously, the second pass is much more intensive, so between the passes, dedicated hardware segments the frame into tiles (mini-frames, basically) and the second pass is taken one tile at a time.

Tiling solves the problem of not having enough memory resources, but to be able to piece the tiles back together into a frame later, the GPU needs to keep a buffer of all the per-vertex data.

Rosenzweig found that whenever this buffer overflowed, the render wouldn't work.

In one of Apple's presentations, it's explained that when the buffer is full, the GPU outputs a partial render - i.e., half the bunny.

As you might have guessed, the partial renders can be added together to create a render of the whole bunny (but with a dozen extra steps in-between, of course).

It turns out that this is because different parts of the frame are split between a color buffer and a depth buffer, and the latter misbehaves when loaded with partial renders.

A reverse-engineered configuration from Apple's driver fixes the problem, and then you can finally render the bunny (below).