Pretty strange effect when viewing in Premiere and Media Encoder. (File is Prores4444 w premultiplied alpha) In premiere if I change the renderer to software ths goes away. GPU is AMD Radeon Pro Vega II 32 GB. THere is a mac Afterburner card installed. So far I see no reason to believe anything is wrong with the files. If I remove the Afterburner card all returns to normal. Also ProRes4444 with straight alpha looks normal.
I had the same experience. It seems to occur in the case of pre-multiplied alpha. Changing the renderer to OpenCL will fix it, but it will be abolished in the future, so I hope it will be fixed so that it can be used with Metal. I have installed 14.9.1 and 15.2, but both are occurring.
system is below. PC : MacPro7,1
OS : macOS 10.15.7 (Catalina) GPU : Radeon Pro Vega II 32GB + Afterburner Premiere Version : 14.9.1 & 15.2
I'm curious what responses and potential answers you'll get. For me, Metal never exports correctly regardless of the Premiere Pro version. I get similar results, and oftentimes green glitches in my exports using Metal, too. I haven't had luck getting responses nor answers on my posts. All that I've found is that OpenCL seems to have a better chance at working correctly. Although, I understand that OpenCL is soon to be deprecated, as noted in Premiere for the past several versions.