Unable to Re-Open Project Correctly

I’m very new to UE4 and I’m attempting to get into it to create 3d video game edits. I’ve run into a problem when I re-open my project, the project is almost completely different. I’ve saved everything, all objects, animations, etc. and these are all saved correctly, however re-opening UE4 changes the look of all these objects. I haven’t messed with any settings and have used all default settings. I’ve been able to render fine whenever I’ve started a new project from scratch, with all objects working perfectly. I’ve attached a few screenshots to show the before and after effect when I re-open a project. Hopefully someone can explain why this is happening so I can fix it!
(hopefully this is the right section of the forum. if not feel free to move it)