RX6800XT GPU hang on GNOME login attempt on kernel 6.8.0-rc1 (only when amdgpu.ppfeaturemask=0xffffffff is enabled)

OS: NixOS Kernel: 6.8.0-rc1 GPU: RX 6800 XT

Upon hovering the mouse over the blue button to login as user, or clicking the enter key to do the same, the GPU seems to hang. I've encountered a ring gfx timeout, but I haven't reproduced this upon further reboots; the hang still remains, but there's no evidence in my journalctl output for it.

Nevertheless, changing the ppfeaturemask from 0xffffffff to 0xfffd7fff resolves the hang.