The span class template synopsis in [span.overview] has this declaration:

~span() noexcept = default;

The noexcept is redundant, as ~span is noexcept automatically. I think the entire declaration is unnecessary as well. There is no additional specification for ~span() at all, much less some that warrants inclusion in the class template synopsis.

Recommended fix:

~span() noexcept = default;

Alternative fix:

~span() noexcept = default;