I also have a segfault that goes away with malloc debugging. Not sure if it's the same issue.

My extension modules are

venv/lib/python3.7/site-packages//_yaml.cpython-37m-darwin.so
venv/lib/python3.7/site-packages//netifaces.cpython-37m-darwin.so
venv/lib/python3.7/site-packages//PIL/_webp.cpython-37m-darwin.so
venv/lib/python3.7/site-packages//PIL/_imagingft.cpython-37m-darwin.so
venv/lib/python3.7/site-packages//PIL/_imagingcms.cpython-37m-darwin.so
venv/lib/python3.7/site-packages//PIL/_imaging.cpython-37m-darwin.so
venv/lib/python3.7/site-packages//PIL/_imagingmath.cpython-37m-darwin.so
venv/lib/python3.7/site-packages//PIL/_imagingtk.cpython-37m-darwin.so
venv/lib/python3.7/site-packages//PIL/_imagingmorph.cpython-37m-darwin.so
venv/lib/python3.7/site-packages//lxml/builder.cpython-37m-darwin.so
venv/lib/python3.7/site-packages//lxml/_elementpath.cpython-37m-darwin.so
venv/lib/python3.7/site-packages//lxml/html/diff.cpython-37m-darwin.so
venv/lib/python3.7/site-packages//lxml/html/clean.cpython-37m-darwin.so
venv/lib/python3.7/site-packages//lxml/etree.cpython-37m-darwin.so
venv/lib/python3.7/site-packages//lxml/objectify.cpython-37m-darwin.so
venv/lib/python3.7/site-packages//coverage/tracer.cpython-37m-darwin.so

Unfortunately I can't test the application without any of these, but maybe we can match my list with fenrrir's.