Implementing Callbacks in TensorFlow using the MNIST Dataset

​My course is Introduction to TensorFlow for Artificial Intelligence, Machine Learning and Deep learning and I have trouble in week 2nd assignment I got zero grade while my answer is correct.

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Please click my name and message your notebook as an attachment. Do include the expanded grader feedback in the message as well.

Notebook metadata is corrupt. Please refresh your workspace and try again.
See Refresh your Lab Workspace section here