Anytime my wireless SB3 has pulled this trick, it was always related somehow to signal strength - I would have to unplug the SB3, carry it upstairs to the PC, reboot the modem, the router, and the PC, then plug in the AC of the SB3, and poof it would work again. Transport the SB3 back to the basement, and it would work again for a couple of days.
In my case, it turned out that the router was not working right - replacing that has caused this problem to completely disappear.
BUT, since you are using a wired connection, it has to be something else - call Slim Devices, I hear they have exceptional support folks to assist you.