I have read the guide How To Run Your Own Name Servers With ISPConfig And GoDaddy although this is on the old GoDaddy platform and things have seriously changed now.
I am not using GoDaddy's Total DNS for my top level domain, I just use the nameservers to redirect it to my ISPconfig server and manage all DNS from there.
I have rang GoDaddy up and asked them to help me set up the Glue records but they didn't even know what glue records are so I gave up.
Now, in ISPconfig 3 panel I should add A records for both the nameservers for each domain/site or just an A record to each domain/site for ns2.mydomain.com only?
For all domains I have 2 NS records setup for each of the nameservers but obviously this is not enough.
The thing I still don't get is, how is it possible that everything was working smoothly for 6 months and lately this problem has came up?