Same issue here on a NUC7i7, had to wipe the SSD to install RoonOS 3, it works fine with TV connected, but as soon as I unplug the TV, it becomes unstable.
Moving the computer back to its rack (where it has been running headless for ages) is impossible, as it would not even boot correctly without a monitor connected.
Please fix ASAP…
Thanks, Christian
Same issue with my NUC8i3BEH. After upgrade it rebooted every minute. Did a clean install of RoonOS 3 (so no roll back for me) which helped a little. Can confirm that its stable (no reboots but music still stops now and then) with my TV connected via HDMI, but as soon as I unplug the TV (or the TV goes in energy save mode), it becomes very unstable.
Very much looking forward to a fix 
It has made me consider buying a Roon Nucleus One. But not sure if the Nucleus owners are better of with this upgrade than NUC owners?
Monitor must be connected, i tried with HDMI cable only and connected to HDMI switch without monitors and it didn’t work.
Until this is fixed, Amazon etc sells HDMI dongles for a few EUR that trick the computer into thinking that a monitor is attached.
Meaby Samsung can ship them for free to all ROCK users? 
Just sayin’, it’s better than rebooting all the time. It’s not all ROCK users BTW, this never happened in Early Access. I have a NUC10i5, for instance
I just want to highlight that in my case, connecting the NUC via HDMI makes no difference, as I described in my previous post …
I bought a 2 pack of them from Amazon UK for about £5 to run on my headless Mac Minis and they worked great. Feels like they would resolve this problem as you said
So … why is Roon not stopping the roll out? So many here with severe problems… and many more without adressing them.
I can‘t remember any update in the last ten years with such an impact.
I now also have no problem after connecting a monitor via HDMI. It seems okay now.
I also can make the rebooting issue go away after by plugging in a monitor/hdmi cable into the ROCK server.
However, this is not sustainable because I don’t have an extra monitor sitting around that can be dedicated to this.
It also works with HDMI dongle connected instead of monitor. I put my old Fire TV Stick to HDMI and it is working for 2 hours so far without issue.
For those of us who’d like to buy an HDMI dongle (thanks for this suggestion @Suedkiez and @Dejan_Marinkovic) to address this, is this just like an HDMI extender or does it have to be an HDMI wifi or display transmitter? I popped one of these deals in for now:
No, none of these. The ones I mean have no output and their only function is to send the same signals back to the computer as if a monitor were connected:
I should have said that “dummy” is the magical search term.
They are commonly used wherever software doesn’t like it if no monitor is connected. E.g., some Apple Minis when running without a monitor limit the graphical output over the network (for remote management) to 1080p. If you want 4K, you plug in such a dummy.
These dummy plugs might be a workaround, but in Norway the cheapest I can find them is 201 NOK + 69 NOK postage with a 6 day wait before then can even be sent out.
I would hope Roon will fix the 3.0 release rather than expecting people to fund a MacGyver solution. That goes against the whole spirit of MacGyvering.
Of course it should be fixed but who knows how long it takes.
Here in Germany, if someone had ordered it yesterday they would have it tomorrow for 5 EUR with free delivery. Better than being annoyed
I rolled back to 2.1.
Yes that’s also an option. I provided another for people to choose 
