Vista guest randomly freezing after updating host Win 10 to Win 10 Creators Update

[folj]

After upgrading my desktop (i-6400, 16GB RAM, Win 10 AU, Nvidia 1060 3GB) to Creators Update, my Vista Basic guest VM has started freezing a few minutes after login (on the guest), on VirtualBox 5.1.22. The guest is not using CPU, or accepting keyboard or mouse input, so I have to close the window & shut down the guest.
Because of sleep issues I updated the Nvidia driver to latest release (381.89), and also tried uninstalling & installing VirtualBox, reinstalling the Guest Additions within the guest, running the Vista guest without & with 2D acceleration, and with & without internet access (Host-only vs NAT), and Display Settings/Personalisation: Windows Classic vs Windows Basic (Basic Aero off vs on).
Before the host upgrade, on Anniversary Update, I did not have these freezes, although I think the version of VirtualBox was 5.1.20 or below.

In spite of these changes, the issue remained, although sometimes it took up to 1h to freeze, while other times it froze on the login screen.

This issue only seems to impact the Vista Guest; I'm simultaneously running a Win 8.1 guest that has no problems.

[folj]

I upgraded to the latest VirtualBox Testing build (v.5.1.23-115172) & was able to run the Vista Guest in a maximised window (not fullscreen) for almost an hour, but when I started my other guest (Win 8.1 - also in a maximised window) & then switched back to the Vista Guest, it froze immediately (or at least that minute, according to the frozen clock gadget). My Win 8.1 guest was not affected by this.

[socratis]

I couldn't see anything funny in the logs, except your screen size, which is not a typical size, because your window is maximized. Try to select a resolution from within Vista, a "standard" one.

or accepting keyboard or mouse input

If you've configured your Vista guest to shut down when the power button is pressed, what happens if you try an ACPI shutdown with HostKey+U. Does it shutdown?

[folj]

I changed the guest display size to 1152x864. I also noticed that SearchIndexer seemed to run at 99% CPU in the guest, so I disabled that service from starting. And in power options I assigned "shutdown" to pressing the power button.
Now my guest still froze (when switching back to it from another, non-virtualbox app window), but this time it was taking 33% CPU on my host (100% in guest, presumably & no disk activity). Host+U did nothing, nor Ctrl+H (Machine: ACPI shutdown), waiting for 5min after pressing them. At 0h38min I tried taking a screenshot with Ctrl+E, but saved it locally, not on OneDrive.

[folj]

In case the guest had some inherent problems (SearchIndexer going at 100% CPU being a symptom), I restored the guest HDD from a backup from a few months ago, when it was running OK on Win 10 AU. I didn't change any settings in
the guest, just ran it as it was then, but with the machine settings same as last week.
I thought I had overcome the problems, but when I rebooted my host & tried to start my Vista guest again, first it froze at the Vista startup logo while the startup chime was sounding (with 32% CPU for 5mins), and then after
resetting the guest (Ctrl+R) I was able to log in, but the guest froze while I was checking the logs in the Virtualbox host window.

Could it be some problems with the audio drivers? I seem to remember that while I didn't have freezing in Win10 AU (host), the Vista guest usually turned silent after a runtime of a few hours?
I'm running the guest with audio disabled, to see if it still freezes (Not yet, at least).

[folj]

No freezes yet after a few hours. The sound on this desktop comes from the monitor, connected over HDMI to the Nvidia card, so if I don't hit any more freezes, it might indicate a bug in the Nvidia GPU driver(?)

[socratis]

I wouldn't have the faintest idea. As I said in several occasions, your logs so far look good, so that may be a possibility.