I’m also interested. according to this apparently in ue4 there’s no support for it.
fortnite seems to have done something but the link is dead.
apparently you can make it work by loading the sublevel in the parent level’s blueprint. by loading on begin play.
eg. the sublevel01 level blueprint load the its own sublevel.
i couldnt make it work though.
https://www.reddit.com/r/unrealengine/comments/dcri4f/comment/f2b0973/?utm_source=reddit&utm_medium=web2x&context=3
I just got it to work, actually. Like I read somewhere, you can manually stream in the sub-sub levels in the BeginPlay event of your sublevel. So, in my example, an object in SubLevel A calls LoadStreamLevel on Sub-Sublevel 1. Seems to work ok.
I could only made this work by having the sub-sub-level to load as a sublevel on the main level. (defeats the purpose).
There’s also this technique, apparently one of the examples could be used to load a level that is not already loaded. or instancing (it only works if the level is not already added to levels tool window)
or maybe this one