Add CAA DNS Records
Originally the implementation of CAA was voluntary: CAs could decide whether they would check for the records or not. However, in March 2017 the CA/Browser Forum voted in favor of a rule that will make CAA mandatory for all certificate authorities. Starting September 2017 all certificate authorities have to implement CAA checking.
I might be wrong, but...
it seems that your name servers are responding with SERVFAIL to all CAA queries.