BIOS didn't help. Still getting the error when I check after an hour or so.
I am running the NUC's display via a DP->DVI adapter (MacMini), then into a KVM switch, which completely disconnects the screens when switched out.
(My desk has three monitors, one which I swap between the NUC and my workstation. The workstation re-arranges the desktop when I select the NUC on the KVM, showing only two screens connected, so it is equivalent to a disconnect.)
I haven't tried to monitor it via TeamViewer/RDP/VNC yet.
FWIW, we're considering to use between two and four of these as parts of our shipping product.
