Wanna share my experience here
My S7 Batch 1 was running fine until I had to reboot ( after 30days+ ) for Hashrate drop.
I had this miner from day 1, never had issues with it.
For no apparent reason my S7 didn’t recognize his boards anymore.
Troubleshoot for 2hours +, swap stuffs, lots of reboot later, turn to google.
Lucky me more people had the same issues and solved it.
The batch 1 didn’t like the latest auto-update ( ??? ) after reboot.
Fix : Use firmware SD-S7-20151211-600.tar.gz
Don’t know how to kill the auto-update, but it screw my miner good.