Running: iMac Retina 5k, 27-inch, Late 2014 Memory 32 GB Graphics AMD Radeon R9 M290X 2048 MB Configuration: Two external displays, both via thunderbolt2 ports. Issue: Running youtube, or any other live streaming video platform and selecting full size blanks the other two attached displays. Same thing happens when I try to run a game - primary display functions, other two go black. If I swipe left I get another "space" but that's not completely ideal either. This seems to have started with Sierra. Solution?