No submodule mapping found in .gitmodules for path

check that you have the proper setting in .git/modules as well. Since a few versions ago, git adds an entry there.

Also, the tree probably has a commit object at that path. To get rid of it you can

git rm --cached Classes/lib/AFKissXMLRequestOperation

that should get rid of it once and for all.

Just leaving this here for anyone using git on Windows. It is possible to follow all of the answers online and still have it not work due to git's handling of path separators. E.g.:

My problem case was adding hugo themes via submodule:

git submodule add https://github.com/danielkvist/hugo-terrassa-theme.git themes\terrassa

will result in a .gitmodules like:

[submodule "themes\\terrassa"]
    path = themes\\terrassa
    url = https://github.com/danielkvist/hugo-terrassa-theme.git

Which will cause problems for git submodule [status || init || ...]

Manually replacing the separators to:

[submodule "themes/terrassa"]
    path = themes/terrassa
    url = https://github.com/danielkvist/hugo-terrassa-theme.git

...solved it for me.

Also solved the deployment on Netlify since they use *nix server images.