VRR only while fullscreen gives ~2 s black screen on RTX 3090 + DP 1.4 QD-OLED @ 360 Hz (open and closed module 615.78.08)

[skullbyte]

System:

• RTX 3090, driver 615.78.08, kernel 7.3.1 (CachyOS), Wayland (Hyprland 0.57.1)
• AOC Q27G4SDR (QD-OLED), 2560x1440 @ 360 Hz over DisplayPort 1.4 (by my bandwidth calculation this mode needs DSC)

Symptom: ~2 s of black screen whenever a window leaves fullscreen or I switch from a fullscreen workspace to a normal one.

Cold-boot tests with the open module (3 fullscreen enter/exit cycles each):

• VRR only while fullscreen (Hyprland vrr = 2): black screen, with both 8-bit and 10-bit.
• VRR always on (vrr = 1): no black screen, but brightness flicker.
• VRR off (vrr = 0): no problem, with 360 Hz, 10-bit and wide gamut unchanged.

So the trigger seems to be the VRR state changing when entering or leaving fullscreen. A config reload with the same mode does not change the VRR state; only a mode change or a cold boot does, which made it look random.

It also happens with the closed (proprietary) kernel module: I built it from the official 615.78.08 .run installer, loaded it by hand in place of the open one (nvidia.ko license "NVIDIA", /proc/driver/nvidia/version without "Open"), and vrr = 2 still gives the same ~2 s black screen on fullscreen exit. So this is not specific to the open module.

Ruled out: the monitor's original cable, PCIe link (Gen 4 x16), and locking the GPU memory clock. The kernel log shows no NVIDIA errors during the black screen.

Similar reports (other hardware):

• https://forums.developer.nvidia.com/t/screen-goes-black-for-a-few-seconds-when-alt-tabbing-out-of-games-with-vrr-at-240hz-on-wayland/314590
• https://forums.developer.nvidia.com/t/linux-wayland-intermittent-black-frames-on-display-with-vrr-enabled-rtx-4090-driver-595-71-05/369187

I am posting this as a discussion because the issue template says closed-driver bugs go to the forums and this one affects both modules. Happy to attach nvidia-bug-report.log.gz or test anything useful.