GitHub folders have a white arrow on them
On your machine, if you navigated to the directory with the arrow and tried to view hidden files, you'd see a .git folder, indicating that it is a repository. This means that it is a repo contained inside the outer repo that you had pushed to GitHub. The easiest way to get rid of the arrow and start seeing your files properly (in my opinion) is by deleting the .git folder. That way, it ceases to become a git repo and is a regular folder once more. Now when you push to GitHub, you can normally access the folder and view all its contents.
Symptom
Check if locally you have a .git/ sub-folder under that folder.
Cause
That would mean the folder (locally) is a nested Git repository, whose tree SHA1 is recorded as a "gitlink" (gray folder with straight white arrow)
What you would then see on GitHub is that gitlink: SHA-1 of the object refers to a commit in another repository, represented by an empty folder name. It is a nested Git repository.
If you see a folder @ xxx, then it is a submodule entry, meaning your own repository has a .gitmodules in it, which records, in addition of the gitlink, the actual URL of the remote repository.
It represents the object name of the commit that the super-project expects the nested submodule's working directory to be at.
In both cases (white arrow with a folder name, or white arrow with folder @ xxx, folder name and version), it is a Gitlink represented a nested Git repository: a placeholder for another Git repository, hence an empty folder. But in the second case, that empty folder would be referenced/visible in a special .gitmodules file.
Solution (to remove the white arrow)
In order to restore that folder content:
submodule:
A git clone --recurse-submodules would restore the content of that submodule in your local repository (as opposed to a nested Git repo, where its URL is not recorded, and the content of the folder would remain empty)
The white arrow would remain on the remote repository, with folder @ version displaying what SHA1 of the submodule repository is referenced by your project.
Nested Git repository:
Alternatively, you could, if you don't care about the history of that folder, delete locally its .git subfolder (assuming it is not a submodule, meaning it is not referenced in a .gitmodules file in your main repository), add, commit and push.
The white arrow would then disappear, and you would be able to access that folder content on GitHub.
Then you would need to delete the gitlink entry:
git rm --cache client_folder
# without a trailing slash:
# not client_folder/ but client_folder
Finally, you can add, commit and push that folder content.
The arrow may mean that is a submodule.
You could try:
git add yourfolder
If that results in an error like:
xxx submodule xxx
appears, you may try this:
git rm --cached yourfolder
Then, you could successfully run:
git add yourfolder