(pre-commit version 2.4.0) We're running in to an odd issue on Windows

$ pre-commit run --files my_file.py
black................................................(no files to check)Skipped

However, running pre-commit run --all-files will correctly format the file. Equally, running pre-commit run --files my_file.py in the same repository on a Mac works fine.

It's like the file is somehow not being read in Windows... Has anybody else encountered this?