I'm not on site so can't check the stats on the actual miners themselves but my hashrates on Antpool have dropped from 30/31ksols average a day (2x Z9 Overclocked Miners) gradually to 22k sols average a day.

Any guesses before I get on site to check?  Weather is hot at around 28deg C ambient but everytime I check the miners the chips are just under 70 temp