unbound refuses all requests

[Daisuke HIGASHI]

   Due to "so-reuseport", enabled by Unbound's default configuration
on Linux platform,
multiple Unbound daemons can be launched (often mistakenly) on the host's 53/udp
instead of "can't bind socket: Address already in use" error.
  In this case queries for 53/udp are distributed to those daemons.

Hauke Lampe via Unbound-users <unbound-users at lists.nlnetlabs.nl>:
> The refusals come from PID 25308 while PID 15016 processes the requests.
>
> Do you have multiple daemons with different configurations and/or a DNS
> balancer?