I solved an issue on another thread, it's closed so I cannot send the OP the solution, so I hope that they see this thread!
Original thread -> Yet another Unbound SERVFAIL with one server - #10 by tanderson1992
The solution is to unblock Russia at the router. I had the same issue with resolving the newshost nzb.su resulted in the event "event:module_event_noreply" in the Unbound server log file. However, sending the query to a DNS server outside of the home network, such as Google DNS or Cloudflare would resolve correctly.
The fix is to go into your router's security settings, and unblock Russia. The procedure will vary for different routers. For Unifi Dream Machine Pro, go into network->settings->Security->Country Restrictions and remove Russia from the blocked list.
If course, that will stop your router from blocking IP traffic from Russia, so keep that in mind before unblocking it.