Hello. Read the whole topic. My Z9 also works for many hours on the developer firmware. And it happens mostly at night, when I can not control it. My Z9 works on Flypool. But many people have different pools and everywhere the same problem. This problem is not in the pool and not in the miners, this problem is in the wonderful firmware !!! As soon as I reflashed my z9 on Antminer-Z9-DEFAULT-500-DUAL-MODE-201808280957-unlocked.tar everything worked just perfect! The hashrate curve on the pool has turned into a straight line at the level of 60 K/sol. Good luck to all.
The same for me. I am trying many setting, but the result is the as described above. Restarting the device is the only way to restore its normal operation. Below is the graph of the work of the rig, composed of two Z9 and one Z9 mini. The Z9 working with your firmware, and Z9mini is witn stock firmware. The problem appears incidently in about 24 or 36 hours. The problem occurs regardless of the pool used.
Devices shows that they are working at maximum speed, but the pool shows that they either operate at a slower speed or that there are no shares at all.
https://i.imgur.com/F4D0RPU.gif