With nvidia.NVreg_EnableGpuFirmware=1 (default value for 555 driver) my system was started normally, but I do not sure that there will be no errors in the future.
With nvidia-open 555 or nvidia closed 555 driver without nvidia.NVreg_EnableGpuFirmware=0 I have another problem Low fps on external monitor connected to nvidia hdmi port · Issue #650 · NVIDIA/open-gpu-kernel-modules · GitHub So now I am using nvidia-open 550 as more stable