I am seeing the same problem with current cosmic 18.10. The stock nouveau drivers work fine but using 'sudo ubuntu-drivers autoinstall' to install either the nvidia-390 or nvidia-396 drivers produces a black screen (backlighting completely off) after the ubuntu splash screen has been displayed on rebooting.
MacPro 2008
GPU: EVGA GTX 680 flashed with the Mac ROM images
I am seeing the same problem with current cosmic 18.10. The stock nouveau drivers work fine but using 'sudo ubuntu-drivers autoinstall' to install either the nvidia-390 or nvidia-396 drivers produces a black screen (backlighting completely off) after the ubuntu splash screen has been displayed on rebooting.
MacPro 2008
GPU: EVGA GTX 680 flashed with the Mac ROM images