I've tried to upgrade the Home Assistant project today to isort 5.0.3, unfortunately, that seems to be not happening.
I've used the following config in setup.cfg:
[isort]
profile=black
indent = " "
force_sort_within_sections = true
sections = FUTURE,STDLIB,INBETWEENS,THIRDPARTY,FIRSTPARTY,LOCALFOLDER
default_section = THIRDPARTY
known_first_party = homeassistant,tests
forced_separate = tests
combine_as_imports = true
After I run isort everything seems fine. However, when I run it again, it modifies some files again, and again, and again...
After a couple of runs, I end up with files like this:

Thanks for reporting! This is fixed in the isort 5.0.4 patch release, with a regression test added to ensure it doesn't happen again
Thanks for the quick response on this @timothycrosley, that is appreciated 馃憤