Or, YACC is still complaining even after I fixed my commit using git commit --amend --author.

YACC checks the commit's Committer information against the Bitbucket Server user, not Author. These are normally the same; however, they will be different when applying patches on behalf of someone else or cherry-picking commits.

Verify the problem by using git log --pretty=full to see a commit's Committer information.

If your git settings are misconfigured, you can fix both the Author and Committer for your last commit:

# Fix configuration
git config user.name Your Name
git config user.email your@email.com

# Reset both author and committer
git commit --amend --reset-author