I have encountered this annoying behaviour of Keyshot 5 sometimes not opening when I start it within Keyshot ST8. It just stays in the initializing state and does nothing until I have to force-shut it.
Usually restarting my system helps and the first time I try to open Keyshot it usually opens just fine, but sometimes after the first time it fails to open. No matter if it is assembly or a part, sometimes it fails and sometimes works, even for the same exact part or assembly.
I just upgraded my workstation to Dell Precision 7510, i7-6820HQ, Quadro M2000M, 16Gb RAM, Windows 10 and have the latest MP8 for SE ST8.