Tax Year Prior to 2020: why is my state refund not taxable?

Hi

I didn't receive my 1099-G. I just follow the turbo tax steps, and it populated my 2018 CA state refund automatically. I went through the steps, but turbotax is telling me that my state refund is not taxable. I don't quite understand why this happens because I had itemized deduction in my 2018 filing. In my previous years' filings, all my state refund were taxable. I am quite puzzled, and I can't find any relevant google search research to explain the behavior.  Could anyone help explain on the behavior? 

Thanks