Unbound cannot register DHCP leases

[mrt12]

Good day,

I am using ISC DHCPv4 and Unbound.
On the Unbound config page, I have configured the following items:

* Enable Unbound
* Network Interfaces: ALL
* Enable DNSSEC Support
* Register ISC DHCP4 Leases
* Register DHCP Static Mappings
* TXT Comment Support
*  Local Zone Type: transparent (this was the default, not sure what it actually means).

I notice that generally, Unbound works more or less fine, is a bit slow from time to time, but it works and can resolve hosts on the internet. I also see that the DHCPv4 server works fine, it gives out leases to my computers on the LAN and it works.
However, I want the host names of the individual computers be registered in DNS so that I can access the hosts by their name. For this very reason, I activated "Register DHCP4 leases". However, I notice unter Services - ISC DHCPv4 - Log file a lot of entries like the following:

Unable to add forward map from <some hostname> to 192.168.20.36: REFUSED

The log is literally flooded with such REFUSED entries.
And indeed, it is not possible to resolve host names on the LAN. I wonder why this is and how I can fix it?
I have seen that other people have already seen this issue, but I found no proper solution so far. What is the cause for this problem and where shall I start digging?

thanks a lot!

[koushun]

I am using KEA DHCP.
I am using Unbound DNS.

I am unable to ping any machines on my network through Ping utility embedded in the OPNsense GUI, when trying to ping the hostname. Pinging the IPv4 address works as expected.

From a client on the network, hostnames does not resolve.

Except the firewall itself, that one works (I can ping "firewall" and "firewall.domain.com" and I get a reply.
This works from both client and from OPNsense itself).

There is no logging besides "Informational" in the Kia DHCP Log File section.
There are no relevant information in the Unbound log.

Register ISC DHCP4 Leases: CHECKED
Register DHCP Static Mappings: CHECKED

System > Settings > Administration
DNS Rebind Check: Disable DNS Rebinding Checks. Tried UNCHECKED here.

Does not KEA communicate DDNS entries?