pytest-metadata was bumped to 3.0.0:

https://pypi.org/project/pytest-metadata/#history

This changed the API for accessing and modifying the metadata object:

pytest-dev/pytest-metadata@v2.0.4...master -> README.rst

With those changes, Environment section is no longer appearing in the htm report (tested on pytest-html 3.1.1 with pytest-metadata 3.0.0)

Also the documentation should be updated to reflect on the changes in pytest-metadata, as this:

is no longer possible