I had a similar problem, coincidentally about the same time as you, except the drive disappeared completely from the network, and I could not reconnect it.
Let me just get to what worked for me. I turned off the NAS drive, waited until all the indicator lights had stopped, removed the front cover, and then removed each drive one at a time, and then reseated it. I had to restart my computer, but wa la, back like nothing had happened.
Good luck