Unbound stops working info: validation failure

[Юрий Иванов]

Hi
Sometimes unbound simply stops serving my clients. (approximatly 15k clients per node)
Today I see this in logs and CPU all 8 cores was 100% utilization:
Nov 30 21:42:16 DNSCache-2 unbound[1515]: [1515:7] info: validation failure ns3.google.com. A IN
Nov 30 21:42:16 DNSCache-2 unbound[1515]: [1515:7] info: validation failure ns4.google.com. A IN
Nov 30 21:42:16 DNSCache-2 unbound[1515]: [1515:7] info: validation failure ns2.google.com. AAAA IN
Nov 30 21:42:16 DNSCache-2 unbound[1515]: [1515:7] info: validation failure ns4.google.com. AAAA IN
Nov 30 21:42:16 DNSCache-2 unbound[1515]: [1515:7] info: validation failure ns1.google.com. A IN
Nov 30 21:42:16 DNSCache-2 unbound[1515]: [1515:7] info: validation failure whiteclick.biz. A IN
Nov 30 21:42:16 DNSCache-2 unbound[1515]: [1515:5] info: validation failure ns8-cloud.nic.RU. A IN
Nov 30 21:42:16 DNSCache-2 unbound[1515]: [1515:5] info: validation failure ns4-cloud.nic.RU. A IN
Nov 30 21:42:16 DNSCache-2 unbound[1515]: [1515:5] info: validation failure ns8-cloud.nic.RU. AAAA IN
Nov 30 21:42:16 DNSCache-2 unbound[1515]: [1515:2] info: validation failure COM.RU. NS IN

One week ago there was such problem too but copu was NOT 100% utilized but a lot of validation failure issues prevent serve users.
When its working there is an IP address instead of validation failure message.
Can you please guide help me figure what's going on and how to prevent this issues?

Thanks in advance.
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