I don't know how my client did it, but something went wrong when editing the Landing page of the site in the builder page.

The result is an unstable draft.

The over-accident is that the display of the full view of the content in the BO crashes the entire page.
While it is only a draft of the object and it has a fully valid published version.

The problem I raise here is the following:
It doesn't matter how corrupted content can become. The BO must not crash.

(Obviously the generation of corrupted content is an important issue but it is not the one raised here.)