Accuracy of C1_W2_Lab_1_mnist.html are much lower than video shown

Course Q&A TensorFlow: Data and Deployment Specialization Browser-based Models with TensorFlow.js
1

In video,

Lectureaccuracy
Lectureaccuracy1135×632 137 KB

accuracy is about 95%.

But when I execute C1_W2_Lab_1_mnist.html, the accuracy is about 60% only. See snapshot below:

RealAccuracy
RealAccuracy1232×721 58 KB

What is going on ? I suspect the data set may have something wrong.