I have two DN2820FYK units.
One is running BIOS version 30 and reboots fine. It does have a problem where a poweroff also reboots the machine but I can live with that.
The second unit had some problems with SUSE Linux Enterprise 11SP3 so I updated the BIOS to version 50. That fixed the problem I had with SUSE but now that I need that unit running Ubuntu, neither reboot nor shutdown works.
I upgraded the BIOS today to version 52 and that made reboot work until I removed power. After powering the unit back up, reboot no longer works.
I know I am not running a 'tested' version, but I think this is a BIOS bug.
We have a similar problem.
We're using Intel NUC NUC5CPYH for a project, with lubuntu 14.04.03.
Sometimes (it's something random) when the pc is going to shut down (or rebooted) it gets stuck at the lubuntu dots animation. If we disable the animation, we can see that it remains at the message :
* WILL NOW HALT
[numbers] reboot : Power down
The only way of making them to work again, is to press the power button manually or to unplug and plug them again to the power supply.
There's nothing wrong at the lubuntu logs.
We have tried different kernels, different values for Intel Idle Max State, and we're running out of ideas.
With the same iso, but using previous NUC DN2820FYKH, we didn't have this problem (and we have around 200 nucs of that model working).
This is something too important for us, because our customers are dissapointed as they don't know what to expect each day.
As you talk about BIOS update, we'll have to try it. Now we send the NUCs with the Bios 44.