Many Thanks for the quick reply, . Typically, it seemed to be a physx version issue. We updated the latest binaries, and I seem to be able to get everything importing now. 
Thanks also for the insight on the bottleneck. So, if a dm has a 0-solid, 1-islands, 2-brick chunks, and I damage that, and in doing so the damage radius causes neighbouring dms to wake, each one of those will wake as a depth 2, effectively?
Also, have you had much luck with fracture maps? I’ve managed to get my level 1 chunks to break nicely, but afaik there’s no way to run a separate fracture for deeper levels.
Best wishes ( and great tutorials vids, btw),