My situation is a bit different, but in case it offers a clue about what’s going on with your posts, I’ll describe as best I can.
I have a static start page and whatever page I set to Posts Page displays as blank (Settings-Reading-Front Page Displays-Static Page). The page looks populated in WP Admin panel, but when you view it from the web, the text is missing, so page appears with menus and blank body.
This site is all static pages, so I copied all content to a new page with similar name and made the static post page private. Any page I set to Posts Page is rendered with a blank body when viewed from the web.
Like I said, I have no idea if this situation has any bearing on yours, but we’re both having issues with “Post” pages.