Grader issue Gradient Checking I received 80%

I checked everything and even the suggestions from paulinpaloalto where he suggested checking this:
Your backward propagation works perfectly fine! difference = 2.919335883291695e-10
Is that what you see?

How I should find a problem. The grader gives a very poor feedback:
“[ValidateApp | INFO] Validating ‘/home/jovyan/work/submitted/courseraLearner/W1A3/Gradient_Checking.ipynb’
[ValidateApp | INFO] Executing notebook with kernel: python3
Tests failed on 1 cell(s)! These tests could be hidden. Please check your submission.”

Please help

Sorry that the grader does not give useful feedback here. Please check your DMs!