Apple macOS 10.12.3 and 10.12.4 have issue to load the devices Option ROM firmware by pressing “Option-Shift-Command-Period” at the Startup Manager window. As a result, your Mac doesn't see ARC-8050T2 that has Option ROM firmware. This issue has been fixed on the macOS 10.12.5 or later version.
Tags: ARC-8050T2, firmware, Mac, Thunderbolt3