Layer 6 was playing with poor performance, so I switched from FFMPEG to AVF. Layers 3,4,5 which were FFMPEG decoder started rendering as solid colors. I restarted M8 and the issue still persisted! (note that there were VTDecoderXPCService processes hanging around across restart). I switched layer 6 to FFMPEG, and now 3,4,5,6 all render as solid colors. I restart M8 again and after restart they render correctly.
mid-2015 macbook pro AMD Radeon R9 M370X 2048 MB
Decoder-related issues have been cropping up since many months ago and I really worry whether I can rely on 3.0