I encountered this issue in #382 . For some reason I am getting this when importing pygeos:

 Traceback:
c:\hostedtoolcache\windows\python\3.8.10\x64\lib\importlib\__init__.py:127: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
pygeos\__init__.py:1: in <module>
    from .lib import GEOSException  # NOQA
E   ImportError: DLL load failed while importing lib: The specified module could not be found.

Complete log: https://github.com/caspervdw/pygeos/runs/3455987095

This happens with any GEOS version, on Python 3.8 and 3.9 only. First I thought it was an issue with setuptools, but I can reproduce it locally (using OSGeo4W build of GEOS) with setuptools 47, 49, 56, and 57 (latest). One question here is: why does Appveyor work? Do you have any ideas @mwtoews ?

With a Dependency checker (This one: https://github.com/lucasg/Dependencies) I cannot find any broken dependency locally.