Just a side note. Not sure which Unifi controller you are using but there is a bug that won't show some of the Ethernet port IP in the UNIFI controller. You can SSH into the router to see all the assigned IPs tho.
@psyvision I had a very similar situation start about 2 weeks ago. I went as far as taking my hub off my main network and plugging only it along with a single PC running a DHCP server into a layer 2 network switch and still no luck getting to 8081 or any other part of the web interface. I mostly did this to try and convince the hubitat team that it was NOT my network. What is the browser error message that comes back? Some things to note about my issue:
I could ping the hubitat hub but could not access any web interfaces
If I left the hub turned off overnight and booted the next morning, there would be a period of time the next morning that I could access the web interface (both normal admin and 8081)
My hub did show up in the portal
in the small window of time the hub was online every morning, I tried soft reset, firmware rollback, and data restore. None of those resolved my issue.
I personally believe the cause of my problem was a corrupted hub at an OS of app layer. Not sure any of that helps but It's interesting to see I'm not the only person to experience an issue like this.
I'm getting absolutely nothing back, it's definitely not registered on the network at all. I suspect the hardware needs reflashing from another PC but I'm not sure thats something Hubitat would assist me with sadly.