I just got a new 27" iMac a couple days ago and did a fresh Windows 10 partition install via Bootcamp. Everything is fine, except I can't get the Startup Manager to load when I do a restart and hold down the OPTION Key. If I used the Startup Disk program and select the Bootcamp partition and restart, the Startup Manager loads fine. If I hold down OPTION when I restart in the Windows environment, the Startup Manager loads fine. However... If I hold down OPTION and restart in MacOS Sierra, then the computer simply ignores me and restarts to MacOS Sierra. I have tried three different keyboards (Magic Keyboard, Corsair K70 USB, another random Bluetooth keyboard)... None of them will load the Startup Manager when I restart MacOS and hold down the option/alt key. There doesn't seem to be an issue with my Bootcamp install since I can restart via the Startup Disk utility, but that's super inconvenient. Anyone else had this problem and how can I fix it?