nslookup on the pihole of a system inside my network but with external name (e.g. pihole.domain.tld) does not resolve to any IP address, if Unbound is used as forwarder, meanwhile changing the forwarder to another internal DNS server, IP get resolved to e.g. 192.168.0.15
So with 127.0.0.1#5353 google.com, test.com etc. is fine, but pihole.domain.tld gets no answer, with 192.168.0.55#53 which is another DNS server (on a synology without any zone files, just like Unbound on the Pihole) pihole.domain.tld is resolved to 192.168.0.1.15 as it should be.