What router are you using? Are you using a tablet? Maybe be a silly question, but have you tried a different ethernet cable?
I have two S1's with Fire HD10's, and one HD7 as master. Performance was usable, but spotty until going static with the tablets.
Sometimes the S1's would be seen, sometimes not. Got IP address conflicts, power cycled things a few times. Eventually things would work, then a tablet would go offline and back on.
Things have been solid for two days now.
