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After a little tinkering, this this problem occurred when Parallel Tools 15 was installed post-PD15 upgrade. I've restored an earlier VM snapshot...
Edit: It appears that kernel.report_hibernate=0 fix also applies to Mac OS (text on that page notwithstanding), but it's not working for me.
I've seen many mentions of this problem with a Windows VM, but none with Mac OS - and the solution only applies to Windows VMs. My Mac OS 10.11...