After upgrading to 5.3, the streaming generation can be non-deterministic between PIE/cooks when using Level Instances in a World Partition level. This only specifically happens when there’s a difference in streaming settings between the main WP level and its Level Instances.
https://dev.epicgames.com/community/learning/knowledge-base/qX85/unreal-engine-tech-note-5-3-world-partition-inconsistent-streaming-when-using-level-instances