I'm currently learning UE4 basis from the Unreal Engine YouTube channel. In this particular blueprint tutorial a Trigger Box is used so that whenever an actor goes inside a small room, a PointLight is lit after 0.5 secs delay. As long as I DON'T build the project, everything works just fine: the room is pitch dark, I go inside, light turns on, I go outside, light turns off. But after building the project the whole room is slightly lit for no reason. The PointLight blueprint script still works, but the room isn't dark anymore. I literally followed step by step the video (and actually you can notice he never builds the project) This is the video I'm talking about
The only way I have to make it work properly again is to delete the PointLight Actor, build the lightning, create a new PointLight Actor, add it to the Blueprint Script and NOT build the project.
Delete any diractional light object you might have on your map, even if its set to 0 it creates a lightmass volume which makes light bounce off of objects and light up the entire scene