Checking the factory, there is no record for this issue and they guess the reason is that after the leakage testing, someone pick up the fail sample and after that put it to the products passed checking by mistake.
We will ask for clearer process and the area for 'bad', 'pending checking' and 'good' should be clear marked to avoid it happen again.
If we have more inquiries of this product I suggest we can try new factories also to have backup source, thanks.