That is a pretty strange symptom that I’ve never seen before. It says “all tests pass”, but then gives you 0 points. One thing to realize is that the “Validate” button in the notebook does not prove that you pass the grader: it just shows you pass the tests in the notebook. But they don’t necessarily catch everything that the grader catches. But then in your case the grader says you passed.
My only theory is that you have accidentally damaged some part of your notebook other than the code itself that the grader depends on. The first thing to try would be to get a clean copy of the notebook using the topic on the FAQ Thread. Then very carefully “copy/paste” over just your completed code from the “YOUR CODE HERE” blocks and see if that helps. Let us know!