Quick answer: Unreal PCG graph rebuild producing different output despite identical inputs? Non-deterministic randomness - seed via the PCG graph parameter, not implicit time-based.
Designer regenerates the same PCG volume twice; gets different placements each time.
Seed deterministically
PCG graph's seed parameter. Same seed = same output. Bake the seed into the volume's overrides.
Or use named seeds
Per-volume seed name; map to a deterministic value. Designers can choose; output is reproducible.
Audit randomness sources
Each random node: deterministic or not. Mixed sources = mixed determinism.
“Randomness without seeds is non-deterministic.”
For shippable PCG content, the deterministic seed is mandatory. Document the seed convention.