Check the configuration in these repositories:
git config user.name git config user.email
Make sure the repo on Mac has the same settings as on Windows.
This thread describes how to change these settings in SourceTree, but check if "Allow SourceTree to modify your global Git configuration file is allowed" set: this means that it will apply to all local Git repositories (Github or not).

The "full name" is a little misleading, as you must use your GitHub login (and GitHub account email) to generate the correct copyright history on GitHub.
Vonc
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