I have a V.5 Pi-Hole with DNS over HTTPS on a ubuntu 20.04 VM running on my Synology DS918+. I have it simply doing DNS as my EdgeMax POE does DHCP but it displays unknown for all devices on my LAN so i'm not able to get any helpful stats.
I did ages ago have an ESXI host which i ran a 18.04 ubuntu VM for pi-hole which was fine but then with a redesign of the home network that was replaced.
I attempted to get a debug token but received the message "There was an error uploading your debug log." even though I can ping a number of websites from the VM.
Pi-hole's main dashboard Top Clients stats, its Query Log and associated stats from Long term data display a client IP address when a hostname cannot be associated with that IP address.
If you see the literal 'unknown' in any of those, that hostname would have to be configured somewhere.
If you are referring to a missing hostname in Network overview, you should be able to relate that information to actual devices on your network by MAC address.
In both cases, missing hostnames would indicate that your Pi-hole isn't aware of any hostnames, as is expected if Pi-hole isn't handling DHCP.
You'd have to configure retrieving hostnames for IP addresses, either by enabling Conditional Forwarding or by defining your EdgeMax router as Pi-hole's only upstream DNS server.
As you seem to be using a Ubiquiti Edge router: Some of those models won't register a hostname as provided by a client during DHCP lease negotiation, so your router would not be able to provide any hostnames.
You may or may not be able to switch your Edge router to use dnsmasq as its DHCP server (see Ubiquiti support for details).
If you can't do so, you could use Local DNS records in Pi-hole to define hostnames. Alternatively, you could disable your router's DHCP server and use Pi-hole as your DHCP server.
The EdgeMax displays the hostnames of my devices (granted I don't expect things like my nest or PS4 to correctly display) and I have conditional forwarding turned on already and the only DNS set in the DHCP is the Pi Hole.
While pondering this today I did remember so oddness with the linux VM when it was running sophos AV which i recently removed (i'm a windows server guy so AV is just a thing I always install out of habit) and in other research somone pointed that in /ect/resolv.conf this should only show 127.0.0.1 but mine has cloudflare dns, does this matter before I start tinkering?
I like having my DHCP and DNS on seperate boxes (again windows guy who likes as few critical services on a single box as I can get away with for resiliancy) but happy to give it a shot if that is the only solution.
You can verify what hostnames your Edge router knows for an IP address by running the following command from a client:
nslookup <host-ip> <dns-ip>
(click for examples)
Assuming your smartphone would live at 192.168.0.42, your router at 192.168.0.1 and your Pi-hole machine at 192.168.0.10, then
nslookup 192.168.0.42 192.168.0.1
would list the hostnames your router knows for your smartphone, and
nslookup 192.168.0.42 192.168.0.10
would list the hostnames your Pi-hole knows for your smartphone.
Note that while there may be more than one hostname associated to an IP address, Windows may return only the first known hostname with nslookup, while Linux will report all of them.