Actors are highlighted grey in the outliner

I have a level with the blueprint classes put into it. The main game is supposed to be started in a blueprint way, I have a widget with a button which upon being clicked loads new level and game mode gets overridden by the game mode that is written in C++. When level is getting loaded, everything I put into it in editor is highlighted grey in the outliner while those actors I spawn in my C++ game mode are fine. I don’t have enough knowledge to fix this. Since level is a collection of actors can I somehow read them from the level file inside of C++ game mode and spawn them from there? Or how do I get those actors that I put inside of a level in edit mode to get spawned?