Can't find anything about this online, but any screen grab is totally washed out, almost as though it is losing a colour channel. Running at 4k/10 bit with the latest drivers on Win 10 64 bit. Any clues?
64 bit Win 10 1903
Benq EW3270U @ 3840x2160/10-bit/RGB4:4:4
Oddly, it had reverted to 30Hz refresh. I've reset it to 60Hz and the problem has gone away...