Windows BSOD in guest upon resuming VM

[JanW]

I have been using VirtualBox with a Linux host and Windows guest for a long time. Recently, I upgraded my host to Ubuntu 18.04, and upon resuming VMs ("save state" previously upon exiting VirtualBox), I now systematically get a BSOD with a SYSTEM_SERVICE_EXCEPTION. This happens on two systems (same host and guest OS). Other than that, the systems run completely stable. If I properly shut down the guest OS before closing VirtualBox, there are no problems.

One point particular to my install is that I set my VM to send fake CPUID information to the guest. I needed this when I upgraded my host hardware to a newer system and the Windows guest detected that the hardware changed, refusing to continue to use the same license. This is a legit Windows license, albeit OEM, which came with my previous host computer. I have not found a different way to make it run on the new hardware, other than copying the CPUID info from the old system and have my VM send that info to the guest. This has worked flawlessly for over a year, and I have no clue if my current problem is related to this.

Another detail: I use secure boot on one of the hosts, and I sign the VirtualBox kernel modules compiled by vboxconfig each time my host kernel or VirtualBox version changes. I don't think there is a problem related to that, all seems to work well.

Details of the host:
- Linux 4.15.0-34-generic #37-Ubuntu SMP Mon Aug 27 15:21:48 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
- Intel Core i7-7700 @ 3.6 GHz
- 32 GB ram
- VirtualBox 5.2.18 r124319 (Qt5.9.5)

Details of the guest:
- Windows 7 Professional 64 bit, Version 6.1, Build 7601, Service Pack 1
- 4 GB ram
- Windows thinks this is a i7-3770 CPU
- Guest additions installed

How to reproduce:
- Boot guest
- In VirtualBox: File > Close
- Choose "save state"
- In VirtualBox: "Start" the saved instance
-> The wait bar of the resume process proceeds as usual to the end, the picture of the previous state is briefly visible underneath, followed by a BSOD

I'll be happy to provide any additional details as necessary to troubleshoot this. And please tell me if I missed existing reports of this error - so far, I haven't found any. For now, shutting down the guest each time I want to close my VM is a workaround, but being able to save the state and resume would obviously be much more comfortable.

Thanks a lot for any pointers!