I'm having the same issue.
What seems to be a temporary fix is going to display settings, selecting another resolution, playing something (for me, it shows an image but a distorted/cut off one at this point) then returning to display settings and selecting your original resolution.
For me that's 4k HDR => 4k => 4k HDR, however even after that it doesn't actually seem to enable 4k HDR (examining the pixels it may actually just be 1080p upscaled, but that also could be the content), it is just able to play content