Thanks Joulinar,
i implement your guidelines & restart the system & after that unbound failure gone, everything normal now.
what you suggest about plex.direct queries to unbound by localhost with plex installation
{private-domain: “plex.direct” } in “/etc/unbound/unbound.conf.d/pi-hole.conf”
as my nuc machine not resolving dns for itself so even if we write "private-domain: “plex.direct” in “/etc/unbound/unbound.conf.d/pi-hole.conf” it will not useful as localhost not using it. so it means for plex local files try to resolve it ip through cloudflare service. any thing i can do to eliminate this and facilitate local machine to resolve local data by itself.