I just bought a brand new iMac as the main computer for my studio and now experiencing similiar but slightly different crashes, often in the middle of recording (both VSTi and audio)! Sometimes Cubase just shuts down in the middle of recording. Sometimes the whole computer shuts down and restarts, no warning, no explanation, during recording. I have both Cubase Pro 9.0.1 and 8.5.20 installed. The same stuff happens in both versions.
I googled a bit around and opened the Console app to look for some answers. I saved some of the crash logs. Some of them are described as "kernel panic". The reason for kernel trap is always described as "type 14=page fault". I have read somewhere that this is memory related. I should add that I have installed OWC 32 GB memory kit instead of Apple's own RAM.
When I get a Cubase crash, with Cubase and not the computer shutting down, the crash logs in Console say this:
I am on Mac OS Sierra 10.12.1, and Apollo Twin Duo Thunderbolt interface. I also have a OWC Thunderbay MINI running two regular hard disks and a Samsung EVO SSD for sample libraries... Could this disk be the problem? I have read that it is not 100% Mac OS optimized since it does not feature "trimming" like Apple's own SSDs do, but it has worked well for me on earlier Macs and earlier versions of Mac OS X.Exception Type: EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: KERN_INVALID_ADDRESS at 0x00000000000016a0
Exception Note: EXC_CORPSE_NOTIFY
Termination Signal: Segmentation fault: 11
Termination Reason: Namespace SIGNAL, Code 0xb
Terminating Process: exc handler 
Because of the kernel panics this may turn out to be Mac OS related rather than strictly Cubase related - but the crashes have so far only happened when Cubase is running, and mostly when recording. I am completely in the dark here, so I figured I'd start out here.
I should add something else that could be important, and that is the way I set up my system. Because of deadlines and lack of time, I took a kind of "shortcut" and used Apple's own "transfer tool" from one mac to another, when I first installed stuff on the machine. I transferred the Applications folder and the user w/ library folder. Just the thought of losing all my own settings in Cubase, or all the references to sample libraries in Kontakt (since I am already using the same sample library hard disk as on the previous machine), the thought of spending a week and setting all that up again... I just couldn't stand it It's possible that the only way out is to completely erase the system drive, and start completely from scratch anyway, creating a completely new user and not transfer any of the stuff from my old machine, but manually installing every plugin and sample library all over again... I just REALLY want to avoid it if I can, because I frankly don't have the time!
Any help any of you could offer would be greatly appreciated... Maybe this is something for Apple Support also...