There is a file that was being tracked at one time by
.gitignore will prevent untracked files from being added (without an
add -f) to the set of files tracked by git, however git will continue to track any files that are already being tracked.
To stop tracking a file you need to remove it from the index. This can be achieved with this command.
git rm --cached <file>
The removal of the file from the head revision will happen on the next commit.