One of those incidents included a Chinese submarine that surfaced voluntarily 5 miles away. I don't think you can interpret this in any other way than as a demonstration of how they can stalk any carrier near their waters at any time without being noticed.
In 2015 a 30 y/o French submarine "attacked" a US carrier as part of a military exercise where all participants should be on the highest alert. In 2004 a Swedish submarine did the same.
I would expect this to be more difficult if the carrier group is on a wartime footing, though.