Okay, I think I found the problem why the culling is not working “correctly”. The issue is that Unreal is grouping hierarchical instances to make it more performant. Those groups are splitted based on the distance of those assets. This works for most cases but fails when you have a bigger map with uneven asset-placement.
I created a quick example for this:
There is the following situation. We have one big HISM for one big map but there is a lot of empty space between the instances
With distance culling enabled, you can see the problem that the grouping algorithm sometimes has. Everything is culled exept a single instance group of objects. This happens because the group is strechted over the entire map.
it probably is clearer when you see it from a differenct perspective. In the image below everything is culled by distacne, except this one group which centerpoint has not reachted the culling distance.
I hope this explains why culling sometimes fails. Culling is not really the problem, it is the grouping that make things problematic.
It would be great if some Unreal Developers would address this issue and may allow an input for maximum radius that the group can have.
All best