Hi Sean,
thanks for the quick reply!
I’ve uploaded this test enviroment project which shows how the level streaming is managed in our project.
I commented all possible BP sections to give more details on how it works.
Anyway, me and my team are working with this project for at least 8 months till now and this issue appeared only by today, this makes me think that the core of the problem is not in how the streaming is manually handled (this also because we came across with this problem even during 4.8 release period and at that time we were using only basic Streaming Volumes to manage sub-levels)
During the day the bug happened another couple of time:
- In the first case it happened after a build and saving the sub-levels
- In the second one instead it was triggered after enabling the visibility of all layers at once (as shown in the screenshot i’ve attached)
As i said it seems completely random 
Just to be very specific the issue seem to be limited to Blueprint Class Actors only.
Static Mesh Actors, Emitters, Point Lights etc. instead are not affected by this bug.
Even more details:
the map total actor count is around 10000, and the average sub-level actors count is around 200-300.
