dnsviz.net: has errors; select the "Denial of existence" DNSSEC option to see them.

[Hans Mayer]

Dear All,

I realized that dnsviz.net is showing me 5 errors for some domain names, 
even some which do not exist.
This is not only for one domain. I see this for some domains I manage.
I am running BIND 9.18.34-dev (Extended Support Version) <id:7c90bd5>

This is for example such an error message at dnsviz:
ok7gd.aw5sp.iiasa.ac.at/A has errors; select the "Denial of existence" 
DNSSEC option to see them.

Searching for solutions didn't really help.
Any idea how to solve this issue ? Or where to dig deeper to find a 
solution ?

Kind regards
Hans

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