Seems to be a bug in 520.56, drm:nv_drm_fence_context_create_ioctl [nvidia_drm]] *ERROR* [nvidia-drm] [GPU ID 0x00000100] Failed to allocate fence signaling event
Please check if this is a workaround:
https://forums.developer.nvidia.com/t/ubuntu-18-04-3-blank-screen-at-startup-with-430-drivers-and-gtx-960/107501/2?u=generix
If possible, please also try the 525.53 beta driver.