Do you see any common event in the AP supportinfo logs of different AP's when this issue was reported? As you mentioned all AP's were disconnected at the same time, were you able to Ping SSH in to the AP's at the time when disconnect was observed? Were you able to login to the ZD from the network when this issue was seen? Have you noticed any port flap on ZD uplink port or any STP event?
I would recommend you creating a support case with above information, few supportinfo files of the AP's and ZD debug log to investigate the root cause. Please do share exact timings on when this outage was observed?