Hellor rbk1234,
The short pause you are seeing is expected when using level streaming because your computer is calculating the assets and lighting information to load. This process is near instant and a useful way to hide the level being loaded is to block the players line of sight. Some games use a loading screen to do this, while others use geometry or a cinematic to distract the player from being able to see the streaming. In your case a short wall extruding out in front of the players view would work fine.
Level Streaming Trigger
In my case I set the level streaming trigger halfway up a hill so the player cannot see the level that gets loaded. By the time the player reaches the top of the hill, the level is loaded and the player is none the wiser as to whether or not it was there before climbing the hill.
Streamed Level
Here you can see where the level is loaded and you are unable to view the trigger volume on the hill. These pictures were took while in the Viewport and not during PIE (Play in Editor) mode. If I press play the streamed level disappears until it is called to open using the level blueprint.
Level Streaming with Blueprints
Above is another method using doors to load and unload levels. Take a look at the tutorial to see if it also helps clarify some questions you may have about Level Streaming.
Cheers,