i have the same issue with an s-7 
I have done some experimenting.
It would appear that the solution to my issue has been to simply manually specify the IP address details.
When I checked
Code:
route -n
I would not have a default route when I picked up by DHCP.
I have set it statically, and all is working well.
It has 9 other S9 miners and 2x S7 miners in the same switch.... None of them had the issue, and I changed the cable... Same problem.
Odd.. Bottom line, it appears to be working now.