I have a laptop running linux with nvidia optimus/intel hybrid graphics where all outputs are connected to the intel card. It is driven by the i915 driver.
An external monitor or beamer is discovered only one time a boot cycle: If I disable or unplug it (and then plug it again), it cannot be enabled again, because the linux kernel does not detect it anymore: There are no udev or acpi events on plug/unplug and the sysfs, in my case
/sys/class/drm/card0-DP-1/status, indicates that the output is disconnected. After a reboot the display is detected again, and again exactly one time. Suspending/hibernating and resuming suffice as well, but only if the output is uplugged while rebooting.
I think this is somehow related to the kernel probing/reprobing for output devices on boot. Can the kernel be somehow induced to re-probe for monitors, and thus to hopefully detect them again?