You can set the author information using Terminal. It might be possible that xCode has the author data but it's not actually set in Git config.
1) Open Terminal.
2) Set a Git username:
$ git config --global user.name "Mona Lisa"
3) Confirm that you have set the Git username correctly:
$ git config --global user.name
> Mona Lisa
1) Open Terminal.
2) Change the current working directory to the local repository where you want to configure the name that is associated with your Git commits.
3) Set a Git username:
$ git config user.name "Mona Lisa"
4) Confirm that you have set the Git username correctly:
$ git config user.name
> Mona Lisa
Source: https://help.github.com/en/articles/setting-your-username-in-git