Resolved Plesk main domain nameserver issues

[Rowan]

So have example.com as a main domain registered with only some glue records at my registrar as following:
ns1.example.com
ns2.example.com
ns1.fire.example.com
ns2.fire.example.com

And my plesk server is registered as fire.example.com with two nameservers and unique ip's:
ns1.fire.example.com
ns2.fire.example.com

However since some days both ns1.example.com and ns2.example.com dissapeared from all the dns queries whilst they still are configured within the dns of my fire.example.com server.

Am I missing something? Did a recent update broke my setup?

With thanks,

 

[Rowan]

Resolved: One of the nameservers didn't contain the same DNS causing a loop of empty and filled DNS