mem temp is the issue crank fans up to 80%, this solved for me

Your 4GB Hynix ram can't handle 2200Mhz of memory clock, the max you can do with the 4GB is 2000Mhz and for many that leads to errors. Some of my 4GB can only run at 1950Mhz even.

Try 2000Mhz and it should be stable and you should get 28.75Mh/s or so. If you get any hardware errors or stability issues then you need to try either 1950 or 1900Mhz. You won't ever get stable at 2200Mhz using 4GB of memory. The 8GB were the only cards which can support memory clocks that high.

I don't like flashing bios so I solved this problem finally.
v12.1 is almost ready, I'm going to release it in 3-4 days.
It cannot perform runtime tuning of memory timing registers, it will be added a bit later, in another update.
But it can apply entire straps on-the-fly (Windows only). Currently for Polaris cards only, may be later I will add support for other cards too. So you can use stock vbios and don't flash your cards to try new straps.
Instead, you just put new strap string to config file and the miner applies it immediately in runtime.
If specified strap is not working it will not cause any problems, after reboot you will have stock strap again because bios is not changed.
This way you can keep stock bios and also test new straps safe and easy.

My firmware version 2.2 for Z9 works with nicehash. Please be sure to use #xnsub.

See my signature if you are not aware of my firmware.

-j

People that think that making money is a good idea.