No DNSKEY record

In /var/log/messages the line

> Apr 19 11:02:11 ipfireAppliance unbound: [4021:0] info: validation failure < A IN>: No DNSKEY record for key while building chain of trust

appears every 15 minutes or so.
I don’t actively browse to that site, so I have no idea what triggers this message.
(I even dislike the site. When I tried to access it via Tor to investigate it didn’t let me access it because of that and advises met to stop using Tor. So no sympathy from me here.)

Does someone know what causes, or mainly triggers, this message?
(Core-Update 174)