You can't rule out human error for working guys at an ATC station....or at a primary military radar.....
Let me tell you a short story, when I served in GAF in the mid 80s. I was a normal soldier which worked shift on a radio support station (GAF) in the upper Bavaria. This station was remote from civilisation, but on a good location where you can operate radio on GHz waves. Our station was also a relay for data channels for example from CRC Freising to Ramstein Air Base, also the former Alpha Jet base (GAF) JbG 49 at Furstenfeldbruck was connected.
Due to the remote location, we had to call the guard post from JbG 49 twice a night, to know them, whether we're allright. During a nightshift at weekend, I did my first call before midnight and all was o.k. . When I made my second call in the next early morning, my call to the guard station failed. Finally I woke up the sergeant and told him what happened. He also didn't get a contact to them. So we decided to phone the local police station, because we didn't know what really happened. So the police went out to air base and found the complete guard soldiers drunken in the barracs, don't ask me what happened with these guys afterwards.....
You see, things happen.... . As a government, I would feel uneasy to admit, that my radar isn't operted well by human error without losing the face
....