Levelstreming Vs. Pre Build (Performance)

Hello I am complete new to Unreal.
I am aming to make a labyrinth.
I want to generate it at the start of the game, so it changes everytime the game is started and I dont have to pre build 100 or more.
So fare so good this works quite well.

I am streaming in wall segments with the levelstreaming.
The issue I am facing is, that the fps drops from 120 to under 40, when the labyrinth gets too big.
First I though “Well it is just too big”, but then I made the same labyrinth by hand in the editor, so pre built it.
The performace issues where gone, fps where around 100.

So where is thre problem, I tried the “place actor by class” node too and faced the same issues, like levelstreaming.

Can some one help me?

Try to place however many pieces you need in a map at design time, i.e. before your game is running. Make them invisible. When you generate, move them into position with your script and make them visible.