The error comes from the foreman-proxy log. The logs in general are not all that helpful sadly but I attached them below. The foreman-local isc-dhcp-server does not spit out any logs at all as far as I can tell. But the dhcpd works just fine for the second subnet. It’s just that foreman cannot claim any addresses. Which causes a bit of an issue with DNS for that block.
I also just edited the /etc/foreman-proxy/settings.d/dhcp.yml to query the second subnet, just in case. But that didn’t cause any changes.
foreman/production.log
2019-11-05T11:46:50 [I|app|] Started POST "/subnets/freeip" for 10.110.5.34 at 2019-11-05 11:46:50 +0000
2019-11-05T11:46:50 [I|app|7512e] Processing by SubnetsController#freeip as JSON
2019-11-05T11:46:50 [I|app|7512e] Parameters: {"subnet_id"=>"6", "host_mac"=>"", "taken_ips"=>["", ""]}
foreman-proxy/proxy.log
2019-11-05T11:46:50 3d4eb815 [I] [2019-11-05 11:46:50.307 #6447] 1 -- Started GET /172.31.102.0/unused_ip from=172.31.102.10&to=172.31.102.100
2019-11-05T11:46:50 3d4eb815 [D] [2019-11-05 11:46:50.308 #6447] 0 -- verifying remote client 172.31.100.1 against trusted_hosts ["foreman.infra.domain"]: verifying remote client 172.31.100.1 against trusted_hosts ["foreman.infra.domain"]
2019-11-05T11:46:50 3d4eb815 [W] [2019-11-05 11:46:50.309 #6447] 2 -- No free IPs in range 172.31.102.10..172.31.102.100.: No free IPs in range 172.31.102.10..172.31.102.100.
2019-11-05T11:46:50 3d4eb815 [I] [2019-11-05 11:46:50.309 #6447] 1 -- Finished GET /172.31.102.0/unused_ip with 200 (1.53 ms)