I write codes and the notebook will give me all test passed, but when I refresh the notebook all my code will fade away, I have refreshed the kernel and notebook 10 times and now I have no idea what should I do

is there anyone who can help me?

I’m not sure what you mean by “all my code will fade away”.
If you click on the “Save” button, it will save your notebook file into your workspace.

After I change the “None” with my code and save it, my code will be graded as 0 and then after refreshing the notebook, I see that some of the same lines in the code that I had replaced are still “None”.

What exactly do you mean by “refreshing the notebook”?

I mean refreshing browser,
now I noticed that actually, the notebook has been frozen somehow for me!

Last Checkpoint: an hour ago Autosave Failed!

this is the message that I got from notebook

That’s very strange. I do not have any ideas what would cause that.