In pypa/setuptools#4474 I report an issue where in the past few days, Setuptools docs builds have started failing due to this warning (treated as error):

WARNING: inventory <https://build.pypa.io/en/latest> contains multiple definitions for std:label:python--m-build--v

I can see that the docs for build haven't changed in the past few weeks.

It's preceded by this notice:

intersphinx inventory has moved: https://pypa-build.readthedocs.io/en/latest/objects.inv -> https://build.pypa.io/en/latest/objects.inv

That makes me wonder if maybe the pypa-build was recently updated to redirect and previously, Setuptools was linking to a stale site and that's why the issue has surfaced now.