We have just been made aware of an existing bug in Python 3.9.7, which causes a regression when using a Dataclass. This has been fixed in the next iteration of Python (3.9.8), but is still a bug in 3.9.7.
Due to this finding, the Bitfount package will no longer be supported for Python 3.9.7, but will be available on all other Python 3.8.* and 3.9.* versions.
For more details regarding this bug, here is a link to the issue on github.