Thanks for the update, El.
I did nslookups on a lot of zoneedit nameserver names, and found a LOT of synonyms:
ns1 is now 45.77.82.193 (same as ns9, t1 and dns1)
ns2 is now 50.116.49.173
ns3 is now 128.199.163.75
ns4 is now 139.162.196.199 (same as ns7)
ns5 is now 159.203.1.67
ns6 is now 45.77.23.227
ns7 is now 139.162.196.199 (same as ns4)
ns8 is now 45.76.95.243 (same as ns13 and t2)
ns9 is now 45.77.82.193 (same as ns1, t1, and dns1)
ns10 is now 45.79.110.158
ns11 is now 37.139.13.54
ns12 is now 139.162.196.199 (same as ns7)
ns13 is now 45.76.95.243 (same as ns8 and t2)
t1 is now 45.77.82.193 (same as ns1, ns9 and dns1)
t2 is now 45.76.95.243 (same as ns 8 & ns13)
dns1 is now 45.77.82.193 (same as ns1, ns9 and t1)
dns2 is now 45.79.110.158 (same as ns10)
The key to keeping your customers' sites from going down is to make sure that they all have two or more DIFFERENT nameservers. Two of my sites went down because, although I thought they had two nameservers, they actually just had two synonyms for the SAME single nameserver.
If you're going to have several names be synonyms for the same server, you need to search your database for customers which have been given those names for nameservers for their domains, and tell them what new nameservers they should use, to maintain redundancy of nameservers. Can you please do that, El.?