There are conflicting reports in the Ars Technica article that makes me think the issue with ZUMA is actually disinfo. They say that the payload fell out of orbit along with the upper stage yet in order for that to happen there would have had to have been something wrong with the F9 upper stage which was reported as successfully deorbiting. I have a hard time believing if there was a problem with the upper stage they would call it a successful flight. ZUMA probably performed a disappearing trick similar to what Misty satellites do. Total deniability.
https:/ /arstechnica.com/science/2018/01/the-zuma-satellite-launched-by-spacex-may-be-lost-sources-tell-ars/