I have a small NUC running Ubuntu 18.04; it has a Dell monitor connected via HDMI which has worked since initial setup.
This week I had to move it from one desk to another and after connecting everything up identically and powering up, the initial login screen was overlaid with a dialog that has never appeared before; I didn't note the exact wording but it said something like monitor not running at appropriate resolution, trying to continue OWTTE. After logging in it appeared to run correctly with no display problems (and at the same resolution as it had always used).
However the next several boots have come up with a completely blank monitor and I have had to access the logs via ssh from another machine. There is no error in the boot log that I can see, but the syslog reports this:
gnome-shell[1464]: meta_screen_get_monitor_geometry: assertion 'monitor >= 0 && monitor < n_logical_monitors' failed
Looking back through the older syslogs I can see the last successful boot - 2 days ago - logging many lines from the gdm-x-session process, in particular listing all the available resolutions on the monitor connected to HDMI-2. On subsequent boots the gdm-x-session process hasn't even started.
Given that the first reboot after relocating was successful, I do not think I have made a mistake with the physical setup/cabling; I'm asking if this problem is more likely to be a hardware failure of the monitor (which is not particularly new or high spec), or some missing or corrupted data/config file?
Edit: I realise that the obvious way of testing this is to plug in a different monitor but I'd need an adapter which I don't have here to do that at the moment.