Published Page Does Not Match Design

I have a page which is not rendering correctly when published.

This is the page as designed:

…and this is how it appears when published:

I would be really grateful if anyone could explain why this should be.

Solved (sort of).

I deleted the entire page and rebuilt it from scratch with exactly the same structure, components and settings. Now works perfectly, cf Bermuda Triangle, Marie Celeste and Lord Lucan.