I'm talking about white specs appearing as soon as I change my resolution to 4k for my PC. Basically seems like the GPU is struggling. There are not a lot of them, maybe a couple of dozen pixels worth scattered at various points of the screen, that pop up in random places even on a still image they'll just shimmer in and out), switching back to 1080p gets rid of them altogether.
The Xbox One S works fine with it aside from HDR which is due to XB1S using 4:2:0 that the TV doesn't handle well at the moment.
I got the Vizio P50-C1. The Vizio CTO who has been regularly communicating with folks over at the avsforums while coming out with firmware updates to fix specific issues, has acknowledged it and has said they are currently working on this issue (and also working on reducing the HDR lag by about 15ms). That update should be dropping sometime in November.
Anyways, my older TV must've had a lower than average color range, because even the SDR content I'm watching on this TV is resolving more detail/displaying more colors (the exact same video files).