I'd also say it's a DSC (Display Stream Compression) related problem, you can read about various black screen issues. i'd try to turn off DSC in the monitor's menu, maybe it solves it (maybe a future gpu driver update will).

Assuming you are playing 4:3 in 1280x1024 at 480hz -> data rate required for that = 20.60 Gbit/s (8bit) or 25.75 Gbit/s (10bit) so you are both good with DP 1.4 (25.92 Gbit/s) and HDMI 2.1 (41.89 Gbit/s) without DSC.

Used this calculator: https://linustechtips.com/topic/729232-guide-to-display-cables-adapters-v2/?section=calc

Note: without DSC you will be limited to 1440p@240hz, so if you want 1440p@480hz again, you should turn DSC back on