to add to speculation, I think it could have been software related, but wasn’t the only factor. My guess is that because we see a bunch of model s’s actually produced and sitting in random places + temp lots at the factory, it has to be safety related for Tesla not to sell them. If it were only software, then those 400+ already produced Model S’s would just be washed and prepped for delivery but they are rather selling brand new ones.
the only indication we have is from Elon himself, stating they needed to test the batteries for “safety”