Does it look like the s11 bmminer is keep restarting? Check the dashboard overview the version of bmminer is not showing.
There are 2 possible reasons why it's not showing the first one may be the miner is not connecting on the internet there is something connection error or blocking your miner to connect online sometimes changing DNS solves my issue.
This is pretty much what i have in mind for now, what's why we need to see if he is getting that "socket connection failed" thing on the main overview, and you are right about changing the DNS, he should diffently try to do that if he is getting that socket failed thing.
I also like to suggest you replace the Ethernet cable you might have a defective ethernet cable.
since he can access the miners, chances that the cable is bad are slim to nothing,but still no harm trying
I suggest you don't touch anything about your miner for now because it is still under warranty so sending it back to the manufacturer is the best solution.
I don't think playing with the PSU cables will void any warranty, but indeed he should not go to the extent that risks voiding the warranty for a brand new Asic.