Why can I only add something to git once?

Currently I am working on The Boredless Tourist. I start having problems on step 6. After I initialize git, add script.py, commit it, and edit script.py, I try to add script.py back to the staging area. When I go to commit it, though, it says:

On branch master
nothing to commit, working tree clean

I don’t know what’s causing this. Checking git status shows that there aren’t any files in the folder, but I know there is. I’ve tried making a new python file or making a text file to see if it affects that too, but I still have the issue. Can anyone help?

Does this StackOverflow post help?

I think so? It randomly started working again for no reason, but thank you anyway!