Hi! I said this with more certainty than I should have. Software can always have bugs! For reference, I wrote isort, and my response came from the perspective that I have certainly worked very hard to ensure it doesn't have any behavior that is random or non-deterministic. From your description, it sounds like someone may have turned on force-alphabetical-sort (if this is in a single project). See: https://pycqa.github.io/isort/docs/configuration/options.htm.... You can do `isort . --show-config `, to introspect the config options isort finds and where it finds them from within a project directory. The other thing I could think of, is coming from isort 4 -> 5, I wouldn't think it would fully ignore import groupings, but maybe it doesn't find something it used to find automagically from the environment for determining a first_party import. If that's the case this guide may be helpful: https://pycqa.github.io/isort/docs/upgrade_guides/5.0.0.html. If none of this helps, I'd be happy to help you diagnose what your seeing.