Hi Dhruba, here's the ticket number - 2165067. I first saw this issue when trying to upgrade my Windows 8.1 VM to Windows 10 following the documented process from your support page. I believe this was left at the point where the support engineer was requesting a remote session to connect to my machine for further troubleshooting. I travel a lot for work, so was unable to dedicate the time to do this.
Since posting the other day, I've tried looking again at this problem with fresher eye's to try and narrow down a pattern. I've spent a good number of hours over the last few days trying different scenarios and appear to have narrowed things down to the EFI option under the Hard Drive advanced options. In a correction to my previous post, my Windows 7 VM does not suffer from this issue (and doesn't have EFI enabled), but my Windows 8.1, Windows Server 2008 and Windows Server 2012 R2 VM's do. These all appear to have EFI enabled by default. I also tried to build a brand new Windows Server 2012 R2 VM as I needed one for testing, and after doing a clean build, this VM suffered the same issue after around the third Windows Update reboot cycle. This VM also has EFI enabled by default. This is the first time I've seen this on a fresh VM built in Parallels 11, as all the Windows 10 and Linux VM's I have for testing work fine. Once a VM suffers this problem, it will never boot properly again until you restore it from backup.
For further info; I did manage to get a copy of all these faulty VM's working by disabling the EFI option and then reinstalling the OS from the ISO file. When disabling EFI, no boot device can be found and startup repair doesn't work, so a reinstall of the OS was necessary. All VM's are now working fine and can be happily rebooted all day long without running in to the 'Processor reset' issue. Hence me thinking that this is a bug when using EFI with the above version of Microsofts OS.
Cheers.