And why is the FAN OUT showing 0 RPM and the miner stops working even if the fan is still running?

If the fan fails to detect the speed, it is decided to be a fan fault.

And why can't we disable the FAN CHECK so that we can continue mining?

Fan failure, high temperature will damage hashboard

And why don't you release a firmware where we can disable the FAN CHECK?

Next version, we are considering adding this feature.

And why is the hashrate to low and so unstable?

Try to reduce frequency.  Some businesses have modified the firmware of Z1, counterfeiting z1+.

And why can't we find/buy hashboards?

We are trying to improve the official website pages as far as possible, and will sell spare parts later.

And why is there so much junk in the firmware?

specific?