Im having the same problem, when i get back in my npc goes crazy and i can target him for 5 seconds then he disappears and i get zoned back in to the CRZ.
I block the new IP i get when i enter deepholm And lets say the ip is : 195.12.243.177, Then i setup the range to block from 195.12.243.150 -> 195.12.243.255.
And iv tried various ways, with 195.12.243.170 ->195.12.243.255 and 195.12.243.180 -> 195.12.243.255