Just adding an observation here to the bug that pages can be non-editable. I also see that for some pages (not clear what is different for those vs. the “good” pages). Not only are they not editable, but their styling is completely of (missing background colors, huge images, etc). This is only in the builder, not on the front end.
I noticed when such a page is opened in the builder as a “preview” in the header builder, or in the Theme settings, then their appearance is normal. So: it is not that the builder cannot properly display such a page in principle.