Unreal Keeps deleting objects from my Scene, how do I prevent this?

So, I’ve been building out a small island castle scene on my Macbook, which was going well. Until one day, I opened my project to find that it had not only not saved any changes, it actively removed certain elements from the scene. I keep trying to rebuild and save it, but it keeps doing the same thing and might be getting worse. The image above shows how the items are being shown as part of the scene. I also tried to create a new scene to rebuild the level, but when I saved the empty slate, parts of the default world came back and were no longer deletable. Is this fixable, or do I need to redownload Unreal again. Thank you for your time.

Were these assets imported from a local drive? Are the assets source models (e.g. fbx files) on your local drive?

Are these objects in the main level or a sub level?

If you are using the world partitioning system the this might help