Same issue following sudden screen blank
In my case, I was actively working. Suddenly my computer screen went blank (the blue that usually immediately follows boot), went to the log in screen.
When I logged in, my computer name had the "(2)." Have rebooted a few times since and it's still there, though there are no other computers on the network right now.
Not sure what the glitch was, but from reading this thread, it sounds like whatever blanked out my computer didn't remove it from it's own imagined network, so when it came back online, it saw a ghost of itself and gave itself a new name = )
I haven't noticed any issues, but will change the name and see if all is resolved. If not, I'll follow-up. If no follow-up, assume all is well.