Hello,
I have a perhaps unusual setup, in that I am using DoT in Unbound, but I am also using overrides to manually specify IPs for some hostnames.
When I first start Unbound, it registers the override (logged as "dhcpd entry changed watch.qt @ 10.0.0.228."), and for about 5-6 seconds it responds to queries for this domain correctly with 10.0.0.228. After that, requests to the server will time out for a short while, and then when it responds again it is with "** server can't find watch.qt: NXDOMAIN" and it remains NXDOMAIN until I restart it again.
General settings for Unbound:
https://postimg.cc/PNNMMrPD