Had mine arrive today, only tested one so far but Nicehash only works for a few mins then doesn't pick up anything and Slushpool gets around 45% rejected shares rate :S
Will test the others tomorrow
BTW yes I have updated the firmware to the latest version
I don't know if you have any other miners or have set up any other ones but:
1) Check your power supply. These things need a lot of good power, a cheap 1200 Watt unit will not hack it.
2) Check you network connection. Could be something there.
If both of them are OK start checking the other miners as you said. If the others are good then it's just this one then it's a Bitmain issue. If the others are acting the same way, post again. There are enough of us here that we can probably figure it out.
-Dave