Unexpected spikes in backend query stats

[BadikovVV]

We're experiencing periodic sudden spikes in backend query statistics (jumping from ~200 to ~2000 queries per minute) on our PowerDNS Authoritative Server without:

Corresponding increase in actual DNS query volume
Increased server load
Network/disk activity on the PostgreSQL backend VM

I looked through all the logs on the VM - no "paranormal" activity of other applications.