Probably many of the issues which are being kept secret relate to matters raised by the Snowden disclosures. They were enough to blow-up the safe-harbour with the US
In my opinion, the actual problems of Safe Harbour were known for well over a decade but were only addressed when it became politically untenable to maintain the illusion, and that was more caused by Facebook vs Max Schrems/Europe than the Snowden revelations. Don't get me wrong, Snowden *massively* contributed to the current EU stance by offering evidence that allowed the EU to stop the usual US blackmail regarding trade agreements, but what ended Safe Harbour was law, not politics.
This is why I also expect Privacy Shield to falter when it is reviewed in July: it is again a political solution, a "we won't hurt each other" agreement to maintain US-EU trade, but the legal underpinning to protect the privacy of EU citizen data in the US has not been established, and I don't see that change, certainly not with Trump in charge. Trump's idea of negotiating is somewhat too binary for this to be addressed, and I have as yet not seen anyone in his team being able to moderate him in any way, shape or form. "Sad" indeed.