if you use a non signed firmware ( like AsicTuner overclock ), it wont work on NiceHash ( maybe not compatible with their "Asicboost" ? ). But if you use original firmware, even the latest, it works perfectly.
To downgare, just recover 1st firmware ( not on their website, they removed it ), put on SD and flash it through the Sd reader.
do you have T17 miner with the latest update and nicehash do work for you ?
Are you sure about the firmware if it's a signed firmware?
if it's unsigned firmware it won't work but if you flash it with sig firmware it should be work.
Anyway, if your miner has an SD card slot you can try to contact bitmain and ask for an SD card image. I'm sure their image is a lower version.
You can follow this guide from here
SD card flashing with customized PWyeah i downloaded it from there website before the last one (i keep all the upgrade files on my pc), strange why i can't downgrade !
i will try the SD thing hope it will work, thank you .