so i have a TP-link Archer c7 v5 router and i was having this problem and decided to just take the leap and flash it with openwrt. This should have resolved it. despite reverse lookups working just fine from the command line to both the router and the pihole. i'm a little confused as to where to look.
root@pihole1:/etc/pihole# nslookup -x 192.168.0.2 192.168.0.1
2.0.168.192.in-addr.arpa name = shark.lan.
root@pihole1:/etc/pihole# nslookup -x 192.168.0.2 192.168.0.3
2.0.168.192.in-addr.arpa name = shark.lan.
ok well the local resolver was set to google, i have reset it to localhost now.
but shouldn't this setting be overridder by the ip address in the dns settings for conditional forwarding?