Thanks so much, Victoria.

I tried. The debug mode enabled. I could see the short code below the builder.
I added the elements one by one, checking every time if the code is getting scrambled or if any unclosed tags exist.
I clicked ‘Update.’ Then the layout appears intact.
But the code disappeared for the new elements. Then I switched to default editor to check the code, which is the same.
Then I came back to Layout Builder, then the elements disappear too.
Please feel free to add the elements by yourself to test it.

Should I try creating a new page and start building from scratch?
Please help.