Please let us know the TAC case resolution on this issue.
My workaround about this issue is based on https://knowledgebase.paloaltonetworks.com/KCSArticleDetail?id=kA14u0000001Uc6CAE
First I checked if DNS security subscription on my firewall is valid.
After I reset the local cache with command "clear dns-proxy dns-signature cache", the error message stop appearing in system logs and the local cache it's regenerated.
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