H.264 Raised black levels

Hi folks, 

I'm seeing raised black levels across all h.264 MP4 files on the latest Switch. ProRes, DNx etc are all working properly. Any ideas what is causing this?

Thanks,

Paul

System: 

Processor  AMD Ryzen Threadripper 3970X 32-Core Processor    3.70 GHz

GPU      RTX 3090
Installed RAM    128 GB (128 GB usable)
System type    64-bit operating system, x64-based processor
Edition    Windows 10 Pro
Version    21H1
OS build    19043.1165
Experience    Windows Feature Experience Pack 120.2212.3530.0