I had similar issues while doing some testing of World Partition specifically (which I think is causing inconsistencies); placing large groups of meshes far apart from one another without any landscape. It became evident that either world partition distance settings aren’t being respected, the documentation for ‘These things are always loaded, these things load based on your location’ is wrong, or the entire measurement system is just outright busted.
You can reproduce pretty easily by just placing some prefabs a long distance apart - the memory barely budges as you move around, and will skew 5-10% with each run.