It is difficult to help you troubleshoot without a good understanding of your network. But I will try to point you in the directions I would go if this was an issue I had. My setup also includes a Windows domain sever that also serves as my core DNS for the windows domain but other OS based devices are not as compliant to the windows ways.
I may ask what you think are questions are not relevant but for me these will help me create a better understanding of your setup. Please do not be offended.
I do not run DHCP on a windows server so this is for sure something I am not going to be able to give you exact guidance on but in general my DNS Service which is dnsmasq has the option to set the default domain but the result of that is that it would register the host name and have a record that has the default domain on it as well. so for a device that has the name of "octopi1" I can look that up in DNS as "octopi1" and know it will also resolve as "octopi1.defaultdomainname".
I can see this in my DHCP lease list. However the only things showing up in my Windows DNS system are the Domain attached devices(Windows devices) and any static records that I might have created there. You should be able to look at your lease list and see what it has there.
Is there a router that might be handing out DHCP and not your windows server?
What is the DHCP server giving the device as a config? Is there a default domain set?
What does your DHCP service show as the proper name for this device?
Did you name your device properly when you installed the OS? The device name is most of the time part of the initial install process but might be by passed when using some more basic script to setup.
Interesting as yesterday morning things were resolving differently for a period.
One device eastron-sdm220 was resolving at .local NOT inverellit.local.
It clicked later that we'd had a power outage for 2 hours overnight, 1:40 to 3:35am.
Backup power held up on the servers & the above Esp device, but Octo & other Pi's went down during that period.
In the morning those devices had the .local suffix.
Later it had reverted to the domain suffix.
Not too that my DHCP Server currently has an 8 hour lease time set.
And it was some time circa that 8 hours that things changed.
No other routers run DHCP. Did have Forwarding running, but that's a year back.
The Server does append the Full domain suffix.
Thought I should be able to use a DHCP option on those particular devices to force .local
but it seems option 015 doesn't achieve that.
As far as that is concerned, both Octo & the Hass Pi were installed from pre-built images.
Maybe relevant to take a look at the host name on the systems in question. It will at least tell you what they expect to be labeled. If its not what you are seeing on the network, it should be a clue that its not the systems themselves. If it is what you are seeing on the network, you can edit it and make it what you want it to be.
Use the "hostnamectl" command to see the hostname of the system. If you think you want to change it. take a look at this tutorial on how to do that.
This is used as part of the mDNS process. It does not use your router to handle the name look up. It uses the Bonjour Service. It might be that your local firewall is blocking this. It runs on port 5353 and requires UDP protocol. If you know the IP and can access it using that, you should be good to go. Just use the IP.. maybe setup a static record for it in your DHCP server so it always gets the same IP, just to be sure. but I would not be too concerned that the "octoprint.local" look up is not working.