Week 2: Mobinet Code is correct but single test-case fails

Course Q&A Deep Learning Specialization Convolutional Neural Networks
1 
 ['Sequential', (None, None, 160, None), 0] 

 does not match the input value: 

 ['Sequential', (None, 160, 160, 3), 0]

This is the error I get in test-case(Exercise 2). If I replace the test-case value with [None, None, 160, None] all the other test-cases pass, and the model trains fine and I was able to achieve ~ 99% on validation set. This makes it seem that the code is fine and does work.

Please help. Please ask if any more information is needed.

2

I was able to fix this.
The problem was with the environment. When I submitted I got a a grader output zero.

Then I opened the notebook again and ran all the cells. This time also I got the error so I thought it was persistent. But the error this time was because last time I replaced the test-case values to my (previous)output values.

3

this time i got 100% val-set acc at 9 epochs. Why is there variation is accuracy when everything have have some random seed?