Streaming Level for heavy logic blueprint

Basically i need to do a loading screen. so i got my Persistent level being used as loading screen and i make it load the streaming level. it works, i can even see the animation on the loading screen for a while, then it freezes…then, when the map is loaded, it unfreezes and works fine.

the issue is the freezing (obviously). as far as i understood, streaming levels load without affecting the persistent level so what exactly am i missing? i enabled the World Composition on the persistent level, move the assets with heavy loading to a different level, add that level to a different layer (with distance streaming disabled, as explained on the guide) but it still freezes. The blueprint that is loading is quite heavy, but even if it would take minutes to finallize executing, shouldnt it run on the background?.

any help please.

used this two guides: