I am developing 3D games in unity using the visual stadio 2019 community.
For some reason, when I changed the code recently, the scene set in Scenes in Build disappeared.
Therefore, every time you run the game, you have to re-register all the scenes.
The version of Unity is 2019.4.7f1.

Ambiguous, but in memory, after copying objects between scenes
I don't feel like this is happening, but the cause is unknown.
Is there a way to fix it?

If i open the Build Settings window when you change the code
The size of the Build Settings window has changed a little, and in English at the bottom right
cannot build player while editor is importing assets or compilling scripts
Is displayed, and Scenes in Build is emptied almost at the same time.

I restarted the editor (Visual stadio) and unity several times.
Also, save the unity project with a different name and load it as another project.
I tried, but it didn't work.

After that, I tried to open a completely different project and change the code,
The scene never disappeared here.

There are no fatal compilation errors, and the game can be executed.

Is it possible for this to happen in the first place?
I couldn't think of anything else to try, so I asked.