it this a legit email?
Yes its legit.
Is it possible for Braiins to ignore a broken temperature sensor and carry on mining?
I have tried to set the fan to a fixed speed, but it didn't work.
I get a lot of I2C errors: i2c: Hashchip I2C read transaction error! Retrying...
Are they from the temp sensor?
Its just errors in communication, can be anything from bad cables, bad psu, etc.
Bad temp sensor either don't show or show crazy values like 200°C...
Yes sensors can be ignored but i doubt that's your issue.