is this a clue ?
2023-07-10T08:57:53.796686Z ERROR bosminer_hal::sensor: Sensor hb7[ii_hwmon::tmp451::TMP451]: read failed: I2C error: general error I2C controller keeps reading wrong address/register
2023-07-10T08:57:53.796753Z ERROR bosminer_hal::sensor: Sensor hb7[ii_hwmon::tmp451::TMP451]: Too many sensor errors, disabling sensor
It seems you switch to Braiins OS, according to that logs TMP451 fail to read the temp which might be the reason why the fans is forced to run at full speed.
You need to find which hashboard that causes this issue and fix the issue by resoldering the chip temp sensor or replace it.
There is no clue which hashboard that caused this error you can run them one by one to find the hashboard with a faulty temp chip.
Thankyou for the SIMPLE but very useful heads up
I seem to have now identified the board causing issue , not sure if i will have ability to repair however
the unit is now running 3 hours without a " FULL ON FAN " issue
( and yes i installed braiins as i need ability to reduce power ( on dark rainy days ) , but increase power on really sunny bright
days as im running these units off of solar