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.
Um, the firmware has a dev-fee built in, 3% which strongly suggests you didn't read the whole topic or there is a language barrier confusion. I welcome you to point out the "many people.. everywhere same problem" with real data and not conjecture, also.
100% positive that is what you are seeing.
I responded 4 minutes after you posted this, which strongly suggests I'm readily available to work with you on any issues you might be having. Please PM me support ID from status page, otherwise and I'll be happy to help figure out whatever it is you have going on.
-j